I have a bigger belly than the FB trainers and I've found that things like mountain climbers (even slow ones) are really hard to do because my belly just physically gets in the way of my legs. Does anyone have a preferred modification or even an alternative exercise I could do that accomplishes the same goal?

All Googling has gotten me is articles about how mountain climbers can help burn your belly fat which is not the main reason I'm working out, lol.