Not selfish at all, you do need to have time to yourself... but a couple of suggestions before you do the gym thing (not necessarily instead of, but in addition to):
1) Breastfeed. Not only is it wonderful bonding time -- even if it's difficult at first, persevere, it's probably what I miss most about my kids being tiny -- it also helps your body to return to "some semblance" of its original shape. Don't expect everything to go back where it was though, childbirth does change your shape (I was stoked to get some hips at last, but my bellybutton ring had to go forever
).
2) Go walking with your baby. It's great for both of you and it gives you an excuse to talk to yourself while you're walking around
3) Sleep whenever you can. If that's all you can think of doing when you have baby-free time, do it. Sleep helps your body get back into its old rhythms and honestly, mothers need sleep more than anything else in the universe except chocolate.
4) Don't worry about your body. It will be gorgeous (once all the floppy bits that have come loose in childbirth sort themselves out) and anyone who expects you to look like a virginal 13-year-old after you've had a baby is either a pervert, too thick to bother with or a nasty bitchy woman who's never had a baby and deserves to have her eyes scratched out. Come to think of it, scratching bitches' eyes out is also great post-baby exercise, go nuts.
And good luck!
