Congratulations!! Ponies are absolutely the best
my girl is a 13.2 hand mix that wears a 66” sheet which is available in most blankets, a cob sized bridle, a 4.5” bit, a 24” Dressage girth, and a Prestige lucky dressage saddle. I buy most of my cheap schooling pads from Horze since many of their cheaper pads come in pony size. My nicer pads come from the Dressage Pony Store, the Collected Pony, or PS of Sweden. My local tack shop can also order from several European brands who mainly do seem to be better about having alternative sizes.
A few more details, I use the Stretchtech TSF girth, which she loves, and did get Dressage boots from People on Horses but she hates boots in general so now I use polos over Eskadron bandages that I ordered from the Dressage Pony Store and Riding Warehouse.
I wish you luck and you should definitely share updates and more photos!