What's the best position to get penetrated / fingered in?

When my gf and I have sex, it's almost always external stimulation. She has tried to finger me a couple times but it was always painful (not that much but still). I think the position is the main problem because I can finger myself just fine and when I do, I'm typically in the shower and not laying flat on my back. So what positions do you recommend for an easier way to get fingered? Or just because it feels good? Or if you've got any tips in general haha