I am normally a size 11 bit of an apple shape with small bum and hips and tendancy to put weight on in my middle so have thickened up round the waist really quickly early on. I have bought a few maternity bits as a size 10 or small and they have fit fine. Gone up to 12 in normal non maternity clothes though x
When you buy online they usually have a size guide, I just measure myself and take it from there (its surprising how much it differs shop to shop).
FWIW I'm what you would call a size 9 then and have ordered some maternity stuff online, maternity clothes are soo big that I'm just going for a size 8 as the size 10 stuff I've got seems way too big for me. So if I were you I'd go with a 10 - or buy both and return one of course!
Thanks for the advice- think I will go for a 10 then as I finally found a shop with a few decent maternity bits (JoJo in Blackheath) and managed to buy a pair of trousers so at least I have something to wear to work and 12 was way too big so I went for a 10.
Did want to do Topshop Oxf Circus but I fainted in the shops last week so not sure if I will be able to handle it if its really busy!