I agree with @katedewind. No stirrup work will encourage a better position and I find that it can sometimes be a little bit easier than riding with stirrups (as in your legs will more naturally be in the position they should be). Also you can get someone to film you ride so you can see what you need to improve on. Then you can have a solid ride where you can just think about what you need to fix. Sorry if this doesn’t really make sense! 🙂
What I do is tie my stirups to my girth with twine for 5 rides. It hurts ur feet at the beginning but it’s only because ur feet aren’t used to it. What it does is it tells ur brain to keep your feet in one spot
I recommend doing a lot of no stirrup work. When you take your stirrups completely off the saddle, you will feel yourself using more of your seat. Remember to use your inner calves and not as much spur. As you are working your horse with no stirrups, you will feel that your legs won’t be moving, since your seat is working. Hope this helps answet your question!