Tumeric is really good if you give 1 tea spoon aday with 16 cracks of black pepper its really good
Do your horse have enough turnout time, if they a lot of the day they will also be stiff. Have you tried HA serum? It's quite a bit less expensive than legend
Also the products from "back on track" are awesome since they work as infrared therapy, so maybe some leg wraps after working your horse. And a back on track blanket or saddle pads for stiffness in the back and hind of your horse.
I use glucosamine for those kind of horses. In the Netherlands we have a brand called Equilin and their glucosamine is the best.
Use MSM they sell it at almost all feed stores and it works amazingly! Get your horse on a SmartPak and add MSM to it
I would ask my vet but I cannot afford constant injections, that's why I was asking about supplements
Sometimes supplements don't work. You should talk to your vet about joint injections. They are quite common and it really helps the horse.
You can also try back on track wraps, those helps great
Try looking at SmartPak Equine ( smartpakequine.com), they have lots of different great joint supplements and a great program for delivery!