First things first, the outfit you made looks really good. Casual but in not boring. I eager to see the final version. The form of boots you made don't really fit to that outfit, at least in my opinion.

Since this outfit is something for the more sunny, warmer days in the year, I would vote for flat sandals. If Heels are unavoidable, I would choose wedge heels. They are my personal favorite form of heels, from the esthetic point of view.