Sleeping on the floor/mattress and knee pain has no established connection however it would be helpful if you answer a few queries 1) what is your height and weight? 2)do you work? If yes how far is your workplace and how do you commute? 3)both knees pain or one knee pains more than other? 4)have u had any accident/trauma previously? Do let me know the answers to these questions and i would diagnose your condition properly and give you a rehabilation plan. Regards,Take care