Best floor mattresses?

My baby was great about solo sleep until 7 months, when we took an extended trip and she realized cosleeping was an option. She hasn’t slept on her own since. We have a super soft bed so I’ve just been sleeping on the floor with her for a few months but she’s 10 months now and my back is absolutely killing me. Does anyone have any recommendations for a decent mattress that’s safe for cosleeping that can just go on the floor?