Word of warning, be extremely careful if you decide to go to Mothercare of Halfords, in fact, any car seat supplier. My other half and my sister are both extremely well versed in child car seat safety and have had very bad experiences in both of the above stores. The supposed trained car seat specialists have been unable to fit various seats correctly when asked to and were unable to answer relatively basic questions when asked.
I would strongly recommend rear facing, by far the safest option as Canonite says. We have a 6 year old who is still rear facing and a 16 month old who will be rear facing until it is no longer physically possible. Our 8 year old only went forward facing last year as she woulsn't fit in a rear facing seat any more.
With regards price, I appreciate that few of us are in the fortunate position of not having to consider money when making a purchase and car seats are not the cheapest things to buy. We've spent around £2000 over the past four years on car seats, upgrading and changing the seats as the children grew and the baby came along. It was a hell of a lot of money to us (to some it's probably not a lot), we couldn't afford it so used a credit card which goes against the grain, but god forbid if anything was to happen to any of the kids, being in these seats would give them the best possible chance of coming out in one piece and minimising any injuries. Some things you simply cannot put a price on, obviously.
The one place we have settled on using is The In Car Safety Centre. (
https://incarsafetycentre.co.uk/carseats-accessories/) The staff genuinely care and unlike most retailers, have actually had the correct training and are fully conversant in the principles behind car seat safety. They are only a small company and unfortunately do not appear to have a branch near Kingston-upon-Hull, but thought I'd mention them in case you happen to be travelling anywhere near any of their branches before October.