You realise you've just started one fo these "my boat's best" threads......
I had a similar story - but substitute an SR4 for your W400, and the length of my garage instead of the pontooons as a restriction. I have a spreadsheet at home that tabulates the main dimensions / capacities of the smaller end of the market, If you can wait I'll go and put a 5M filter on & paste the results here later / tomorrow. Alternatively search the threads- I have posted a selection of small stuff before.
Altrnatively as a Kick- off try the Humber O- Pro 2m Beam (there's a 5m one in the narrow width, can't remember if they do a 5m in the 2.3m beam version); Ribcraft 4.8; SR4.7 Searider;
I'm sure more people will be along soon to add to the list......