Really soft bed required as existing bed too firm

Hi, I am a side sleeper who likes a really soft bed. For years I've had an old mattress and a fairly cheap foam topper from eBay which has been fine (although topper is quite saggy now). Recently bought a new house and a new mattress (pocket sprung - medium) but it is much too firm for me. I've tried lots of mattresses in shops and I think I'm very particular! I really want something soft that my shoulders sink into - right now when I wake up I have to re-click them into place. Will one of your toppers work? Can I return them if not soft enough?
Kind regards