we were recommended maxi cosi cabriofix car seats for our prem :) I would always choose carrycot option too, I was so worried about my prem if she had been forward facing in the buggy I would have spent lots of time stopping to go and check she was ok! lol

Congratulations!

I would definitely say getting a double you can use carrycots on would be better than a Nipper in my opinion. If you decide to get a Nipper, you can put rolled up blankets in the foot of the cocoons so that the babies don't wriggle down. I did that with my daughter when I used a Graco soft carrycot at home for her to sleep in. You can usually attach soft carrycots onto the seat so that they are still facing you so the Nipper could be an option. I think I'd prefer an Easywalker Sky Duo myself though. Their products are extremely good quality, whereas Mountain Buggy have been seriously slipping in the quality stakes recently.

I'd be looking at a carseat that lies quite flat, but not a carrycot style that fits sideways in the car-they're not as safe as standard carseats. The flattest I've used is a Silver Cross Ventura Plus (Here for £45) I think my second choice would be Britax Baby-Safes (Here for £55).

Congratulations! I would either stick with the Nipper (get the new one or the old recline will get annoying with two babies), or look at the Easywalker, Twinner Twist Duo or Baby Jogger Elite above the Duo TBH. Those first three offer far more in comfort, quality, function etc. The first two have carrycots and can take car seats. As others have said, you could always pad out any carrycot or cocoon to stop a baby sliding down, but I haven't seen a baby slide in a carrycot yet - or maybe I don't go down any steep hills You could look also at Bugaboo Cocoons as they have a head support area, or Petit Zia soft cots too for any of these pushchairs. I was impressed at the Britax Baby Safe SHR-II Plus (I think it is!) car seat at the way the seat lies flatter - the back angle moves. It's very comfy. But if you want to use it as a travel system then you need to consider compatibility etc.

congratulations, i had the easywalker with double carrycots with car seat adapters and maxicosi car seats i also had a mountain buggy (old style NZ made) with twin carrycot. i did love the twin carrycot on the mountain buggy, my twins loved being together and it lasted alot longer because there was more room. the easywalker was great as a travel system, it is fantastic to just click the car seats in and out of the car and onto the chassis of the buggy when you are popping out and the babies are sleeping. the maxicosi car seats are great and recommended for premmies because they have a padded foam insert. mine were 3 weeks early but one twin was only 5lb and he was ill so lost alot of weight in the first weeks, we were in and out of hospital with him so the car seat was used alot and it was great for him. both the easywalker and mountain buggy are great off road, we used them both regularly in the woods and on the beach. there are some great bargains on e-bay like this MB twin carrycot for £25 www.ebay.co.uk/itm/Mountain-Buggy-Double-Carry-Cot-/170710295986?pt=UK_Baby_Pushchair_Accessories_parts_ET&hash=item27bf2065b2
also look at the width and weight, the nipper is wider than the MB but the nipper is lighter. the mb is 73.8cm, easywalker i think was 75cm, the p&t sidebyside is 73cm, the width was important to me as i had a door to get through that was 74cm.