Happy medium between comfort and good gas mileage to haul?

This is really hard!! For better handling, we need to stay 20' or under! But, we have not seen anything comfortable that is 20' or under. The only one so far, that we have seen, is a 25' 4,200 lb FF.

The 18' is a not a walk-around bed, and we just do not and cannot be climbing over each other to get in and out of bed. There is one more dealer around here, but it seems that lightweight, small TTs are very hard to find...especially with walk-around beds! Used is even harder!