I think the key thing to focus on is that as long as your child is happy, then it's win win really - more money, chance to remain up to date with your professional skills. Maybe it's different if you're stacking shelves just to earn a crust and there's no job satisfaction, but a profession is different - there are a lot of upsides to keeping your hand in.
It's tough when like Caz, you're not getting enough sleep. I found that when I went back to work after maternity leaves, my babies slept better though. I think the routine, getting up at the same time every day, having good stimulation during the day etc really helped from that point of view - tbh my children were better sleepers than many of my friends kids. They also dropped their day time naps earlier, which made me wonder if there can be a link with working - when I was home all day on maternity leave I couldn;t wait for nap time to break the day up a bit, which maybe meant they weren't so tired at night. If your baby is happy and stimulated during the day, hopefully she will be ready for a really good night's sleep, leaving you with some evening downtime with your partner.
I always enjoyed going back to work - I loved my time off, but I think I enjoyed it all the more because I knew I had a good work life waiting for me too.
It is hard work, no denying it, and tbh I think being at home is easier as you don't have to fulfil other peoples' expectations, but I think once you get over the fact that you're going to be busy, there's a lot of upsides to working, and not just the money!! I also found that among couples I know who both work, there does tend to be a more equal approach to parenting and to home stuff, which suits a lot of people. I'm not saying you can't be equal when one of you is at home, but it's inevitable that you'll tend to polarise your roles, with one of you being 'earner' and one 'carer' and you probably have to work harder to dispel this stereotype. Whereas if you both work, you tend to fall naturally into both roles.