I did it.
Everything everyone is telling you not to.
I volunteered for redundancy, had IVF as a single woman, it failed, found anther job took 3 years to adopt went back to work part-time, gave up work when I became ill and DS needed me more, went back to work blah blah blah.
Luckily I didn't know about MN so no-one tried to talk me out of it! My mum and sister were all in favour.
It's tough as shit at times. But it's no tougher than for any other single parent. Bieng hard up is no fun but as you've paid your mortgage off that will make things easier.
I don't think in your late 30's peoples opinions will matter, you will go ahead if you want to and you will have to plan it so you won't be bumbling in blind like so many people do.
I do second the opinion that as you've had a bog shock give yourself a certain amount of time to think things through first.
When I broke up with my ex I gave myself a year to decide and plan properly - in the end it only took me 6 months and I was ready.
Best thing I ever did - even with all the challenges (and at the moment they are legion) I would give up an arm before I would give up on the time I've had with DS so far.