Can i get the same results doing ab exercises lying on a bed mattress compared to excersising on a hard floor? i still feel the burn when on a bed.

Depends: It would depend upon the type of exercise you are doing. If you are trying to do exercise specifically for your abdomen muscles, i believe it would be best to support your back on a mat of some type. Your spinal ligaments and muscles would be active in many exercises that would otherwise work only your abs. Result for many exercises would be exercising both groups, i.e. Abs and spine. Thanks....