Try the UK car seat group on Facebook - they'll be able to recommend the best seat based on your baby's percentiles. Lots of seats that are sold in the UK are only very minimally tested, so best to get a safer one!
We recently got the Joie ispin 360. It works perfectly but it isn’t the lightest if you’re having to switch cars
We got cusynsafe from Halfords and so happy , it's roomy and leather around will be easy to care for in the future