Sub and disabled

So the other night my husband/daddy ordered me to get on top. Now I have no problem with this if I'm having a low pain day and even on some low pain days it's hard. We understand each other and our limits, but I was wondering if there was a way I could do this more. Like if there was any device or someway I could do that even with my weak legs. He's totally fine when I can't and understands I just wish I could do it more for him. Being a sub makes me feel empowered and makes me feel good so if I can please him even more than I already do that would be an awesome suprise.