Hi OP, I will return to work in a few weeks time when my baby is exactly six months old. Of course I feel guilty about this decision although I suspect a mothers' lot is to feel guilt no matter what the situation.
As others have said, see how you feel once you have the baby. Do your research, perhaps get a care giver in place and tell your empoyer when you think you'll be back but know that you don't have to specify when you're going back until 28 days before you wish to return. This gives you the leeway to see how you feel - you may want an extra couple of months.
For me, I didn't know how I would feel when the baby was born though I was fairly certain I would want to go back and as it happens my baby is gorgeous, happy and easy going and I am having a blast on maternity leave. That said, I'm also aware that what I'm living at the moment doesn't approach "real life" and I need to go back to work. This is partly financial, partly for me and partly for the baby's benefit. I believe that the longer I keep him at home solely with me, the harder it will be for him to adjust to a change so it's either go back soon, or not until he's pre-school age by which time my career and earning prospects will be ruined. For what it's worth whilst this is the choice I've made, I think six months is a tiny bit too early, an extra month or two might have been nice but this is the way things are so...
He'll be at nursery, Mon-Fri 8-6 though I'll be working from home 2-days a week and DH will be working at home 1 day a week. We are also getting a cleaner (this was non-negotiable!) in order that we can devote weekends, holidays and evenings to the baby and ourselves. For the baby, well instead of a slightly distracted Mum in a house with limited space and limited toys he'll get to play with new things and other babies every day and I'm pretty sure they'll be feeding him a wider variety of food than I could ever think up!
Whatever anyone says, happy parents = happy baby so you do what's best for your family. Working full time and nursery may not work and if not I'll reassess. I'm certainly not going to continue with something that makes him miserable.
We were all brought up to work and most have done so since we were in our teens; I can't see how anyone can belive it's an easy decision to make to give up everything you have ever known in order to achieve some modern ideal of the perfect stay at home mum.