T. - a good rule of thumb is if you are going to make less than $25,000 you aren't going to come out ahead. There are numerous studies out there and you can spend hours reading through them and calculating, etc. - but the industry general rule is 25K - this is if your chid will be in full-time care.
You mentioned "extra income", which leads me to believe you are not in financial straits and would just like to pad things. If this is the case, consider just working part-time and see how you do. It is a hard decision, emotionally, and every mom is different. For me, it was never a question of NOT working. I love working. And I make good money. I could not be at home everyday as I don't have the stamina for that. I started off with nanny care and eventually switched to daycare. the care you find will make the difference. And the type of care doesn't matter, it's the people. An in-home daycare may let your child watch television all day, and a nanny may talk on the phone all day, and a daycare may not have structured activities. So there are cons to every choice - they are all GOOD choices,though, and only you will be able to know the comfort level of the typ of care you choose.
Maybe without even getting a job you can enroll in a mother' day out or find a daycare that does part time care and just for a few weeks try it out. See how you do, how your child does.
It's an agonizing decision, for sure, but just remember it's not permanent. You can change your mind. If you do work, give it at least a month to help you with separation anxiety and then decide if you like working. I wish you lots of luck!
S.