Booster Seat

Our 3 yr old has almost grown out of his carseat so we are looking at buying a booster seat but there are so many out there it's hard to decide. I think I want one that can go into a half booster as he seems to be tall. I would like to keep him harnessed for longer but from what I've read pretty much all booster seat only harness till 18kg which is 1-2kgs for him (although he's been the same weight since October last year so could be longer away). We will need to buy 2 so can't afford to spend too much on them.
Can anyone recommend a good booster seat please.