Lowrance may be the way to go.
The problem is not the brand, it is the SI function.
The Lowrance transducer for side imaging is far larger than the humminbird SI transducer. ( Unless they have come out with something new and smaller very recently.) it is around 10" long and has the same mounting requirements as HB. I actually like the lowrance transducer better than the HB, but it was just too large.