Wow. Thank you very much.Are you using the weight disks like a foot stool to lift your legs up higher? It sounds like your shoulder straps may be too short. When sitting, your accordion should be able to rest comfortably on your left leg for support without raising your legs. Watch THIS VIDEO and see if it helps you.
However, that video is for a piano accordion or 5-row CBA. With the narrow keyboard on a three row button accordion, it is possible you may not be able to press your right leg against the keyboard to keep the accordion from moving to the right when you push the bellows. In that case, you may need to depend on your left shoulder strap, and/or use your thumb against the edge of the keyboard AS THIS PERSON IS DOING, who is not even using a left shoulder strap. Experiment and see what works best for you.
I noticed a long time ago that my 3-row accordion gets a very short treble side. If I sit in the "standard" position with opened legs, it just cannot reach my right leg. Unfortunately, everyone talking about holding an accordion has a piano accordion or 5-row CBA.. The issue of mine is just unspoken. You are the first one to mention it, as far as I know.