I agree, you may be a good candidate for a made to measure jacket. Standard sizes have a set chest to waist sizing and it's typically the chest that is bigger (I think 6" is a common difference).

If you're going to spend the money on the jacket, spending a little more so that it fits right is money well spent. A well made jacket will last a LONG time, and since it's a traditionally styled Prince Charlie, you don't have to worry about the style changing.