Compact 5point harness toddler car seat

I have been looking at buying DD a toddler car seat soon so that the new baby can have her car seat. ATM, we have a SnS 'Guardian' and 'Safekeeper'. We only have a medium sedan car and would rather not have to buy a new car just yet if we can avoid it, so we are trying to find a seat that will fit into the back without too much trouble! So it needs to be a compact seat. (I will look at getting the baby and DS new compact seats if necessary, but thought getting DD one would be a cheaper option for now!) I would like it to still have the harness in it because DD (who is 3 1/4yrs) is still only just 14 (ish)kg. I did wanted to get a SnS 'Maxi rider' but looking at reviews it says that it is quite wide. I want a seat that will last her til she's at least about 5 or so, so I don't have to buy another really exxy booster for her later. And preferably nothing costing over about $2-300.

Any suggestions??

maybe ask ~trish~ what she has in her car, as she fits 3 kids in a smallish car

Yeah MaxiRiders are quite wide. We have a Rav4, so not a wide car at all. The 3 seats we have are: DD1 will be in a Infa Secure Ve Lanti Adjustable Booster Seat, DD2 will be in a MaxiRider, DD3 will be in a Go Safe Ether Convertible Car Seat
The Infa Secure & Go Safe were the slimest seats we could find.

We just bought an infa secure car seat for DD1. it cost us 180 including the 5 point harness.
its really slim which is why we went for it. we'll have 2 baby seats plus the booster so needed something skinny!
good luck