Hi, I really need to buy a new mattress as I'm waking up very stiff and in a lot of pain in the mornings. I don't want to make an expensive mistake choosing one though as I'm not sure whether to go for a hard or soft one. Which is best for posture? Tbh at the moment the thought of a hard mattress makes me grit my teeth but if it'll be best in the long run... Any advice would be appreciated, thanks .