I'm commenting because I literally had the exact same question while having some fun an hour or two ago and I'd also like to hear the answers people have to this question.

I have plenty of things that I can make due with, but they're all juuuust awkward enough that it takes me out of a good headspace after a little bit. It's either a weird angle, not secure and moves around, or makes me put my legs in a horribly uncomfortable position that hurts after a few minutes. Part of my issue is probably that my go-to medium dildo is a bit cheap though because the suction base on my BD toys aren't as much of an issue with sliding around.