Hi Loiroi,
A mattress protector is important to protect your mattress from stains and the body fluids, skin cells, and oils that we release each night, to protect against spills and accidents, and to keep your sleeping surface in a clean and hygienic condition. It will also protect your warranty because most mattress warranties are usually voided with any type of stain on a mattress. They can be easily removed for washing and are usually designed to have the least possible effect on the feel and performance of the mattress itself.
A mattress pad is generally thicker than most mattress protectors and can have a more significant effect on the feel and performance of a mattress. While there is some overlap between them … there is more about mattress protectors and mattress pads and mattress toppers (which are thicker yet) in post #10 here.
It sounds like your base would be similar to using your mattress on the floor so it’s unlikely that it would be the cause of any issues you may have with a foam mattress.
The height of a platform bed or support system is just a preference choice and will make no difference to how a mattress feels.
Phoenix