I think you'll find the limitiation with the very light end of GA is that of payload. For example a C42 can only lift a total of 180kg. It's fine if you want to fly solo, but put two 90kg people on board and you are left with 3kg for fuel! And that's before you factor in things such as luggage and the general detritous which accumulates in most aircraft.
I suspect that most replies will suggest going down the LAA permit route in something like a Jodel as they can be good load-lifters with more sensible running costs compared to spam cans.
So probably a good starting point would be to consider what the a/c would normally be expected to carry - that should narrow the field a bit.
Oh - and don't forget - you'll have to make your own coffee ;-)