Get one second hand. All the colours this/last year are dull dull dull. The ones from a couple of years before are much more colourful. And you save money.
If you get a Kiddy, Maxi Cosi, Joie, Cybex or Recaro car seat you can put it onto loads of different prams just by getting "Maxi Cosi adaptors" (aka universal adaptors)
If you go for a Britax, Graco, Mothercare, Silver Cross, My Babiie, Ickle Bubba or Kinderkraft car seat/buggy you can only use the same brand.
Cosatto I think are in the process of switching so they do maxi cosi adaptors and their newest car seat works with those as well.
It is IMO worth researching car seats as this is a much more important piece of equipment for your little one :) and extremely confusing. There is a good Facebook group called Car Seat Advice UK you could join and read through some of the posts (or do a search for infant carrier) to see what people do and don't recommend.
Big wheels/good on terrain vs lightweight, easy to maneuvre is a trade off. You get more of one you sacrifice the other. But those were both things we wanted too and these were the in-betweens we managed to come up with which didn't cost a million pounds (my other essential criteria were: parent facing seat, proper lie-flat (hinged seat, not moulded one that tilts), and small enough to fit in our miniscule boot).
Maxi Cosi Stella/Adorra
Cybex Balios S
Mutsy Evo (second hand only) - this is what we got
Joie Chrome DLX
I was doing this research a year ago now so options may have improved compared to these ones. I noticed MN have rated a newer Maxi Cosi one as even better, which might be worth a look as I don't think it was out last year.