Miss E - I have a 21 month gap between DS1 and DS2. I got a double pram (mountain buggy) which I used whjen i had them both. It didnt get heaps of use to be honest but it was awesome when I did use it (we are now selling it). I used thebugaboo for DS1 when I was alone with him (DS1 was in creche 3 days and I did most of my walking when I just had DS2 in the end).
That said, my boys arent really into prams - so I dont use either anymore!!! (so if your DS is still in the buga you prob would get more use out of a double IYKWIM)