Origins Comfort 1000 or Origins Pocket 1500?

Hello. I’m after a new mattress to put on my platform base, as the mattress I bought several years ago for a bad back (quite a firm bed) has now become rock solid in feel to me. I can’t see any noticeable indentations, but I assume the filling has flattened and, as a side sleeper, I now feel like I’m sleeping on a plank and am waking up with an aching back and shoulders most mornings. Reading through one of the earlier questions, I came to the conclusion that for a softer feel mattress – keeping hold of my platform base – the Origins Comfort 1000 might be a good choice for me, however, I like the sound of the wool upper layer on the Origins 1500. I weight about 9 stone and feel like I would like the softest mattress possible. Would you recommend the Origins Comfort 1000 or the 1500 for me please? If I got the 1000, I could put a wool topper on it, if necessary.