Hi peaches, just been having a look 4 you, if you google transversus abdominus it will come up with a few sites for you - dont try any of the sit ups mind you!! The most helpful one is on postnatal exercises though the babycentre.co.uk - pelvic floor, tilting, transversus, unlikley youll manage the push up and on the leg slides you have to really concentrate on keepin your pelvis still otherwise it will tip form side to side and cause you pain - dont try and slide too far out.
Otherwise dont rush out and buy new mattress, the hips pain are usually ligamentous and if you feel you need something softer try folding a spare duvet to put under you, you may find the pain remains though, normally the only way to reduce is to keep changing position. Try using a pillow between your knees and sometimes a folded towel in your waist helps if on your side. On your back the floded towle in the small of your back and pillow between knees (be warned though there are a small no of women whose BP drops in this positon - if light headed turn over), if you are normally a tummy sleeper this can still be done by placing a couple of pillows above and under bump.
Try and avoiding asymetrical activities ie, standing on one leg, opening legs to get in and out of car and bed, avoid high impact activities, if swimming often the spinal position in breast stroke is a problem so may have to stick to back stroke/crawl. Cut down on long walks or try using a support whilst doing. You can purchase a proper one on fizziostuff, physiomed sites (and others) but initially get your partners leather belt and do it up firmly around pelvis/under bump then go for wander, if going to help will be fairly spontaneous, if dosent help dont waste money buying one.
You could also try ice packs over the sij, but if you cant do anything else do yourpelvic floor lifts as these will help to stabilise from the inside and static tightenings of your stomach and bottom.
If not responding to anything it probably is worth getting checked out, the human body is a funny thing and lots of things can mimick each.
Wow that turned out to be a pretty long answer, good luck, hope it all settles down for you. Sorry prob lots of typos