As the title suggests I am searching for a car seat for occasional use as we don't actually have a car.

So just wondering if anyone can suggest a convertible carseat (i.e. newborn-18kgs) that would be most suitable for someone in my situation? I don't expect to use the seat very often, only really when I go on holiday or on the odd occasion I go in a friend's car or use a taxi as we generally just walk most places. Special considerations are;

-something that is easy to fit in any type of car so it is safely fitted each time it is used
-I suppose something fairly compact (especially in rear facing mode as I will use it in this capacity for as long as poss) so that I won't have a problem fitting it in a variety of cars
-it must have good side impact protection

Thanks in advance for your help!