Never owned the breed - so cannot really give you any sound advise - I believe they are often referred to as gentle giants though and love being part of a family - you do not mention the sex of your smaller dog - assume that you will go for the opposite sex should you decide to get one of these.
all I can say is do your homework and look for a good genuine breeder - unless you are considering a rescue that is.
youvre probabler already done a lot of research
regards
DT
welcome to the forum by the way
English Mastiffs And Bull Mastiffs: This Is One Gentle Giant