In reply to ginaj:
I would advise you go to a specific climbing shop. Everyones feet are different and it is beneficial to have someone really good at boot fitting help you get your first pair. You want them to comfortable and very supportive, all the different boot manufacturers use different lasts to build the boots, as such each brand will fit your feet differently. You may find in-experienced (but enthusiastic climbers) who work in shops like decathlon may try to convince of their opinion ( this is often to get you to buy very tight shoes).
I have worked in a specific climbing shop for 3 years and have been taught a huge amount about fitting boots by my peers, but now I can always feel positive that what I have fitted is correct. the same can be said for my colleagues. I have how ever had countless numbers of customers buy shoes who come in complaining the boots they got elsewhere were too tight or hurt despite being large (because they got the wrong shape last for their foot).
The shop you go to should stock at least 4 manufacturers so you can try a range of boot shapes. I would recommend would be a good independent, try:
peak/sheffield/manchester try Outside
N. Wales try V12/Joe brown
Lakes try Needle sports
London try Urban rock
I know the staff to be good at all of these shops.