I was dreading the return to work when DS was 4mo, but by 11mo when I did go back it felt a lot easier leaving him. The difference between leaving him at 11mo and 4mo is huge - he was down to morning and evening milk feeds so I could keep bf going, takes solids really well, and is at an age where he likes exploring and meeting other people.
I have a very similar set-up to what you will have: good degree and very well paid job with flexible employer, and fortunate enough to have a DH who earns just enough for me to be a SAHM and is supportive of whatever I want to do.
I've gone back 3 days a week, and although the adjustment is hard (I'm a month in) and I have worries about whether I really have a career at the moment or just a job, I feel fairly optimistic about it at the moment. I get to carry on with what I worked so hard to achieve (and what would be difficult to pick up again in a few years), yet have all the benefits of 2 days just with DS when we carry on activities we started in mat leave.
DH and I decided I should give it 6 months to see how it goes. We picked 6 months as I'll be free of any obligation to my employer then over enhanced mat benefits so any decision is free of encumbrances about having to pay money back etc., but also because it is a decent amount of time to make sure that DS is happy, and that I'm happy.
Really, truly, don't make any decisions now: you really don't need to. Just enjoy your time off. And then you should think about giving your 3 days a week job a go for a few months - you may love it as you get to continue your career (albeit at a slower pace), but also still have weekday time to do activities with your DS.
The reason I say that is because it sounds like you are in the very lucky (though in some ways hard!) position of having a choice. I am too, and decided I needed to try going back so that if I decide to be a SAHM then I will know it is because combining motherhood and career didn't work for me. I wouldn't want to have the what-if questions about my career if I hadn't tried to combine the two, and I wonder if you might feel the same later down the line.