Raincoat recommendations for a bulky dog?

I have an adorable rescue dog who is a mix of staffordshire bull terrier, border collie and French bulldog. She hates going out in the rain, and her unusual body shape is making it nearly impossible to find harnesses and coats that fit her. Harnesses are always loose at the front and tight at the back, right at the limit of their range on both ends. If we find something to fit her chest width, it is always too long for her little body. Does anyone have recommendations for coats and harnesses for bulkier dog breeds? Or perhaps where I can get something custom made? We live in the UK, but are open to ordering from anywhere