Which mattress for us

Hi we need to buy a mattress. He weighs roughly 90 kilos and I around 50. He likes medium firm and I like firm. We have a slatted Base bed which measures 160cm wide and I've put a board not this to get a firmer feel to a miserable Dreams memory foam mattress that is more of a nightmare than a dream. We are saving money to buy a decent nights sleep and your advice will be much appreciated.Marion