My bullie has been on Royal Canine Bulldog 24 since she was 11 months old. It is a little more expensive than the dog food which you are currently using. I buy mine on-line. It costs just over £40 with p&p for a 12kg bag. However, that does last around 3 months.
Before this my baby was on Royal Canine Sensitivity, which is only available from my vets, and was £65. She is much happiernow on the bullie food, i do highly reccommend it. Pets at home do have this in stock if you want to do a trial. It's just a 3kg bag for around £16.
I hope this helps as our bullies have very sensetive digestive systems