I agree with the others, get down to your target weight before you go ahead with the operation. I say this as a 38K, I'm waiting until I am a healthy weight before I look at my options (also as my mum tells me, you have to be a certain weight before they will operate, so have no choice in the matter!). My mum had a breast reduction due to having breasts a similar size to me and now that she's lost lots of weight her boobs aren't very big at all, I think she regrets not trying to ditch the weight first.
Also, have you thought about getting them done on the NHS? You could ask to get put on the waiting list now, lose the weight you need to lose to qualify for the op and then when a place comes up for you decide if it's what you want to do.