My recommendation: Shop around and decide on a travel trailer. THEN, decide on a tow vehicle that can handle it adequately. If you settle for a travel trailer and your tow vehicle is at its limit already, you'll not be happy. For instance, my wife and I bought a 5800 lb travel trailer to be towed by a Nissan Frontier with a 7800 lb tow rating. Once the trailer was loaded, I would guess it was closer to 6800 lbs and, while the truck could tow it, it wasn't a fun tow. We ultimately traded in the Frontier for a RAM 1500 with a tow rating of 11,800 lbs and it is a total different experience. It handles better on hills, handles better in wind, much better ride and I don't feel like we're pushing the limits of the tow vehicle now.
As far as size of travel trailer - one size doesn't fit everybody. It really depends on the individual(s). Consider not how it feels in the travel trailer when you're shopping. Consider how it would feel in the travel trailer when you've been stuck in it for two days in pouring rain (that's gonna happen from time to time). But, once you decide on a travel trailer, it is easy to match a tow vehicle to the trailer. If you do it the other way around, you'll likely end up with a travel trailer you're not happy with.