It is not an easy decision - and one you do not have to rush into. It is such a personal decision too. Unfortunately people seem to forget all the thoughtful consideration that mums put into their decision making processes. Just make sure you leave room for any changes. I had some supply issues once I returned to work - this was complicated by a very unsupportive team and environment, I found this really distressing and felt like a complete failure along with all the other stresses of returning to work when I simply couldn't express anymore. I can be a control freak and was under quite some pressure at the time due to changes within the work place.
Just make sure you don't put too much pressure on yourself....you have done and will continue to do a fabulous job, no matter what happens.
You are a champ - that is one spunky boy in your sig. Remembe to celebrate the successes you have daily too!!