I'm happy you are enthusiastic and get good results, but I did not invent this. I only learned it, so don't make me blush, ok?

Another thing you can do is convert to duotone. You can't access duotone in one movement though. First, after having played with- and got your greyscale image, you have to switch to greyscale mode( Image>Mode>greyscale) and then, in a second step, you can set to duotone (image>mode>duotone). Here you have the option to choose between duotone (two colours) tri- and quadtone (three and four colours) In fact these are created for printing on offset-presses, mainly to use ink / colours whose hues cannot be mixed with the basic cyan, magenta, yellow and black, but you can use them to your benefit. Even for internet display.

Choose for example duotone (tri and quad work the same, but with additional inks, so you simply repeat this for the other inks.).
In the dialog, you see "black" and an empty  rectangular space below it. Doubleclick there, and a dialog opens where you can choose a colour. This colour will be mixed with black. Choose one, and say  "wow" (necessary!). Try several untill you find what you really like.

Then you can doubleclick the small curve that's on the left of the colour in the duotone dialog. It will pop-up, and you can adjust like you fancy. Don't be afraid to try out some weird curves. You'll certainly be inspired.

When you get a result you like, switch back to rgb (image>mode>rgb)

This way, by choosing a second colour, you get a far more rich result. Because when you use only grey, your three channels, r,g, and b are identical. This reduces the possible hues. By choosing a second colour with a barely visible hue, not only you can get a result like old photographs, but you get different information in each channel, which leads to richer results.

and the cherry on the pie is that when you use four inks (quadtone) and you set your curves in special ways, you can get subtle hues depending on the lightness of the photo. "experiment" is the verb that applies here.

Now if this isn't fun!

There are no Borg. All resistance is fertile.