resulka we have the aquapod, just the single one. It is worth every penny, although the duck thermometer is to be ignored! Do you intend to breastfeed? Most people find that their periods don't return until they pretty much give up breastfeeding, although its not a guaranteed method of contraception blah blah. So when DS1 was 12 months, it took dropping down to pretty much one feed per 24 hours to kick start my fertility again, got first period in nov last year, was careful that month as didn't want an aug baby if could help it, and fell pregnant with this bean in Dec. So DS is currently approaching 20 months, and will be 22 months when bean arrives. He is still sitting in the seat now, and there is no issue on him fitting in it, there is plenty of room to spare, and he still has no awareness of danger and definitely still needs to sit in it for now, but I think by the time bean needs to go into the aquapod seat, DS1 will be fine to sit on the mat on the other side. I would add that i have found it horrid being pregnant with a toddler, mainly due to my back/pelvis issues, and would recommend a longer age gap if time is on your side, as i think if DS1 was say 2 1/2 now he would understand far more, and life would be a lot easier. So unless you are hell bent on having them very close together, i wouldn't bother with the double pod.
loup23 re what to put a baby in, we have a vibrating bouncer which is good for getting them to sleep, and intend to get a musical swing this time too (wished i'd got one last time but never did). DS1 would never sleep in the day unless he was held upright, and the vibrating bouncer helped a bit, but i heard so many good things about swings that we are willing to buy one in the hope it makes life with 2 a bit easier! For when bean is 4 months onwards, we have a jumperoo - which is one of the best things we bought for DS. Hours and hours of fun, he never got bored of it, and if he wasn't too heavy for it, he'd still use it now!
Re play pens, we have a babydan one, which can go against a wall to create a playpen, or be used as a fireguard. We also have a graco pack n play, which can be used as a play pen or travel cot and is good for using in the garden as it has UV covers. Initially we used the babydan one against a lounge wall to create a safe area when he started to crawl (until he crawled he had a play gym - one of those arch things with toys dangling down). When he started to pull himself up, the babydan one was used as a fireguard and we babyproofed the lounge, and the graco one became like a den - we leave the zippable hatch open so he can crawl in and out of it. We also have a cheap travel cot from kiddicare in our room, which has toys in it, and i would put him in there when i needed to have a shower, toilet trip etc, so that he would still be where i left him when i came out! Still use that now, as there are times where you just need him to stay put for a few minutes!