Easiest/Laziest positions?

Ok so I have PTSD and NEAD which basically makes me extremely exhausted. When we have sex I can't ride him neither can we do doggy style, because it takes too much energy out of me and can make me sick. So we've just stuck to missionary, which is lovely in its own way, but also I have always liked being 'top' too, we are sort of 50/50 balanced in that department. I don't know that many positions so I was wondering if any of you girls can help me out with positions that would make it easy on me or positions where I can 'top' but it's still easy. Thanks!