Considering buying an origins pocket 1500

We're considering an origins pocket 1500 mattress and hoping to buy asap; and if at all possible receive the mattress by Sat 9th Jan? However, we also want to make sure that we've made the right choice. We trying not to pay more than £600 and both prefer medium/firm mattresses in terms of support. However, we do like the feel of a softer/luxurious topper for comfort. Both of us have had niggling back issues. I have had issues with my lower back muscles because of too much time at a desk/computer with incorrect posture. My wife is currently pregnant (25 weeks) and had an existing issue with the lower vertebrae (frequent yoga resolves this but she is finding it more difficult now that she's reaching the later stages of pregnancy). If you have any suggestions regarding our current decision to buy a King size Origins Pocket 1500, we'd love to hear them before we buy. Kind regards, James and Mindy