Oh, I wish I hadn't had to go back to work after having DS and I'm so hoping I'll be able to spend longer as a mummy before having to work again this time round.

It sounds like you're not entirely sure if it's right for you - and in the end only you can know. Is there any chance of making it part time or job-share at all? You might find that easier to manage. Or else, if you feel you really need something different for yourself (and that's fair enough), maybe look around for something that would fit better - ie, shorter hours/fewer days.
Your son's at an age where he might really enjoy and benefit from some time in care with other kids. Full time might still be a bit much, but a couple of days a week maybe? Again, you'd know best.