I would look into a purebred Section A stallion. Small and extremely typey. They can often trot with a little too much knee but when crossed to sportier mares; they sire beautiful movers. The Section A will improve the topline, keep the bone you desire, clean up the head, and keep it pony sized.
Your mare is very pretty IMHO and I think the cross with an A will do very well
Choose something that is a proven sire of what you are looking for; just don’t go out and pick something because it’s cheap and looks nice. Look at the offspring and judge from there
My Choices for you:
Smoke Tree Kismet. 11.2hh, great temperament, sire of show winners, older quality bloodlines
Falling Moon Merlin: 12.3 from Telynau bloodlines. Many of his offspring are competing in the pony hunter breeding arena right now. Fancy, clean heads, quality movers.
Farnley Magic Word: 11.3hh from deep Farnley bloodlines. Stunning stallion in person. He is very balanced, true to type, small enough for you, great athleticism.
Ceulan Lwcus: An older stallion who is also 11.3 with lots of chrome. Very typey.
Wharley Magic Flute: 11.2 Palomino Section A. Affordable and very fancy stallion.
Severn Gambol