Is there an existing animated pose or BVH that will help with this,
or should I just keep experimenting?

Not sure if step 2 is suppose to be the final pose?

Otherwise i would suggest that you decide how long you want the animation to be and start by adding the first pose as in step 1and then add the final pose next. And then work in all the key frames, starting with the hip area as that is where most the movement will come from, dont worry to much about the legs, then get the chest to follow the hip, dont worry to much about the arms either, maybe just move them into a position where you would like them to be, but without being to precise, when you have the chest area moving correctly, then you can work the arms/hands, and adjust the chest if it doesnt work well with the arms. 
When you have that in place and are satisfied, it should be fairly easy to get the legs and head moving along. And then you can finally go in and adjust things where they might not work exactly as you would like them too.

I agree with the above poster.  The hip will start the movement as the character sets it up to use as a fulcrum to begin moving the trunk of the body to the desired position.  IOW, the hip moves because the chest/shoulders/legs are about to move.

If the hip appears to be in a position that will already support the main body trunk for movement to a new position, then it may not move or move noticeably.  ie: A figure lying directly on its side with the widest, most stable, portion of the hip usable as a fulcrum for the rest of the body may not move the hip much at all during movement.  But, if the hip isn't set within a good margin of error, then the hip will be adjusted ever so slightly to provide stable support as the rest of the body begins to move.

Look at where the center of mass is and then where the force of that mass is going to be centered.  Everything will depend on that center during movement.  If it is off, then the force will "force" a change.  If you don't see that change, then movement doesn't appear natural. (IMO)  In your animation, the character must absolutely depend on force and a suitable fulcrum on which to apply it in order to change position.  Of course, it's possible to use a less efficient fulcrum due to preference if the character actively chooses to move differently. (See Dancing/Gymnastics/Skating/etc)  But, doing so while simply lying in bed would be doubtful.

Note: Every movement is dependent upon this.  So, once the hip is no longer the most efficient/natural fulcrum-center, then there will be a new one and the rest follows from that.  It's actually a pretty complicate process that we all take for granted.

You want to know for sure? Easiest way: I guarantee it --

Get in bed. Pu the blanket over you.

Turn over.

Note what your body does, what the sequence is going to be. Everyone does it differently, so listen to your body.

This is how old-school animators do it. It'll work for you as well.

Agree with Sean on the try it yourself; I know people who roll from the hip, dragging the upper body along, and those who roll from the shoulders, those who find their place in the matress and basically just plant their arms and legs and turn in place, sprawl optional. Having said that, she looks like a 'spin in place' kinda girl, as she doesn't move from her position. Maybe start the roll from the shoulders, so she can see the star. That gives you the start to bring the knees up together (and if you do it right, you can use the knees to slide the covers back and down, leaving the hands free. Once the blanket is over the knees, a little back and forth of the knees will work the covering down the shins). That will get her on her back, arms free, and knees bent.

I agree with SeanMartin above.

Also if you got a a small camcorder, or webcam, film someone in the bed turning over and check it as you work on the animation. Is the small details that add realism.

Most animators have a mirror in their desk and check their own expressions when working out lip-synching, etc. They check and film each other and themselves constantly to get the right movements.

Yep - that works. Even better would be to have the missus (hubby?) do a practice run while you observe it from the sidelines.

'course, as mentioned, everyone does it differently. For instance, I usually move my head first as everything else follows it. Others may move their legs first, or arms, or ...?

For future reference:

After monitoring my own wakeup this morning, I find the action is
five "snaps" or jerks, each taking about 1/2 second.

1. Topside arm goes up to clear the blanket for room to turn.
2. Chest and head turn about halfway (mainly by abd twist) leaving hips in place.
3. Hips turn about halfway, with a slide to resume same location.
4. Chest and head turn the remainder of the way, again with a slide to resume
   location.
5. Hips and legs finish the turn, pivoting on the chest.

One thing Poser lacks, which would make moves like this a lot
easier, is the ability to set a pivot point dynamically.   Many human
actions require holding one part steady.  It would be
really nice if you could tell Poser to treat the chest as pivot
from frame 15 to 36, with soft leadin and leadout.

Quote: "One thing Poser lacks, which would make moves like this a lot
easier, is the ability to set a pivot point dynamically."

Something that  can help in situations like this is to place a prop so that its origin is where you want the pivot to be, then set the figure parent to be the prop. Now the prop can act as a extra pivot point. If you need yet another pivot point, load another prop, position it,  then set the parent of the first prop to be the new prop. Not as convenient or flexible as a dynamic pivot, but it can sometimes get you out of a jam. Of course you hide the prop.