I have similar worries. No family nearby, I need to work part time, DH works long hours and isn't terribly good at helping out with the nitty gritty stuff. Some chronic conditions and I'm 40 next year. My pregnancy was awful and I have acquired two more things health wise to manage now.
But I do keep thinking that having #2 when ds1 (terrible feeder, sleeper, very hectic busy always on the go or incredibly clingy, and very determined little thing) is older, a second will be a little easier. He's 3.5 now and some things are getting easier anyway. The school he'd go to is directly behind us apart from anything...!
A friend said she'd always wanted two and so wouldn't ever let anything stand in her way.
When I think about imagining how I'd cope as a single mother it seems to help me be more resourceful. DH does help, much more now, and tries very hard when he can but has struggled with the life changes tbh. He really wants another.
My biggest fear is getting very ill again (I was very weak) - simple things like loading the dishwasher were impossible. Coping with the business and mess of two scares me in that situation.
Both sets of parents are late 60s, early 70s too.
But, I know I'd regret it if I didn't.
That said, my back up plan/ therapy is a dog (I think it would be good for all of us and ds; I grew up with lots of animals and digs) and several friends can't have children anyway, so I'd count myself lucky.