No idea about the kids thing. However, if pregnancy is that hard on your body, I would strongly recommend letting it have more time to recover. I can't remember which month DS2 was born in, but he must only be a few months old, your body isn't back to 'normal' yet y'know? I understand wanting to have them close, but you also need to keep yourself healthy so you can look after them properly.

Personal experience - I am the eldest of 4 girls, all born within 4 years. There's 18 months between me and my first sister. Growing up we got on well, and generally went everywhere together. Now that we're adults we don't see each other at all, but that's for personality and religious reasons. I get on better with my second sister, who is 24 to my almost-27. I think it comes down more to personality once the kids get older, rather than age gap.