I have recently purchased a mattress that is medium firm believing it would be right and unfortunately my partner and I both experience upper to mid back pain when awaking, I believe this may be due to the mattress being too firm.I am 6 foot and weigh 14/15 stone but my partner is 5 foot 2 and weighs about 7/8 stone.We are unable to afford a entirely new mattress but believe a mattress topper would be the solution we are looking for.What could you recommend?