bruised knees after girly push-ups

I'm not strong so I cannot do regular push-ups. But when I do girly push-ups I always get bruised knees, even if I'm only doing 10 on a yoga mat. I can't do any on the regular floor cause it hurts a lot, and if possible I actually do them with my knees on a pillow. Anyone else has this or any ideas on how to get round this? (Besides doing real push-up, I'm working on that already but will take time)