I don't think it's too small a gap...I fell pg with DD when DS was 12 months old and he was 21 months when she was born. It has worked out well for us, although of course those early weeks can be hard, but I think that is the case with any new baby. I actually didn't mind having 2 in nappies, it is not too hard to change two at once, the only thing is the expense of buying two lots of nappies (probably not so much of problem if you use clothies though).

If you want to do it - go for it!