I changed nubs while on maternity leave and started new job whe. Dc1 was 8 months old. It is a demanding job and I carry responsibility, I enjoy that though. Having an interesting job where I can achieve helps me be a good mum, being at work often feels like 'me time' and when it's going well I come back to DC1 (now 15 months) refreshed from having expressed that side of me.
it is well paid, flexible and my new boss sought me out to hire and said 'I know you are a first time mum tell me what you need to make this work'. I work four days a week with one of those from home.
You need to do what's right for you, that will be right for your family. There's no 'should' about it.
Can you explore what you are worried / feel guilty about a bit more? If you're happy and your son is happy and it works for your family, great! Well done you.
If something isn't balanced well, you might be able to negotiate for more. They chose to hire you, be confident in that and don't make unasked for sacrifices - will they really care or notice when you go on maternity leave, or how long for? Most employers are well aware of their obligations and are at least philosophical about it.
We plan another and this time, now I'm in a better more secure job I will take a year off and enjoy it. I will likely be very loyal to this job as they are being good to me. That's a great benefit for my employer in terms of my commitment to go back and recommit after DC2 comes along.
I think you maybe need to be more confident in your abilities and choices and worry less about what other people think. I'm sure that's what La Sandberg would tell you!