I have the Maxi Cosi Loola Up & it collapses in on itself when you fold it up, so very compact. I have a seat ibiza & can fit it in my boot, plus some bags & the parcel shelf still in. I'd recommend having a look at it & try it for size! x
Ps. You can get a carrycot to go with it, which we decided to buy 2nd hand (thankfully) because we never really used it! The seat folds right back horizontally, so with a cosy footmuff, baby is lovely & snuggly!