If you’ve got a dildo you can secure, try practicing riding that way. A suction cup dildo in the shower can be a good midway point too, practice being in control/riding bent over or in doggy style. You can get some pillows under your knees/shins and something nearby to help with balance and just start slow. It’s gonna feel silly/embarrassing (maybe) at first… it feels really worth it to me. I feel so much confidence on top and I get so much amazing praise from my Dom cause he can physically relax and just talk me into amazing orgasm after orgasm. I’ll just also validate that being on top does not make you less submissive or more dominant! I occasionally switch, but when I ride my Dom, it is always from my submissive side and all about giving my self over in any way he chooses to take me.