The answer to selecting a full timers trailer very much depends on personal makeup, living style, the type of travel and very often the number of traveling pets.
Virtually every non-RVer we know has a reason why they can't fulltime, "my makeup kit won't fit".. "Where do you store matching outfits?"... "no room for my 3 dogs"..."what do you do when it rains?"... It goes on and on. You just can't explain the fun of full timing, the being out 'there' not carrying the burdens of everyone you know. We're entering our 13 year and it's only in the last year where close friends and relatives are coming to recognize the fun we're having. Miraculously we've had almost 100 months of shared vacation seeing North America in the last 13 years.
Fiberglass trailers extend from 13' to 25'. Each size has people that travel happily and extensively. The bigger trailer you get the more you move to virtually a small home on wheels and that's definitely OK. You have to get what fits your style, body type and probably most important your partner's needs.
To full time, more important than the trailer, takes a 'mind reset'.
The names of the big fiberglass trailers have been listed. My suggestion would be to attend a fiberglass rally
or two. Most of the people will not be fulltimers but will provide the opportunity to feel out the various rigs.
In my opinion truly comfortable sitting doesn't happen until you get to a small fifth wheel or small motorhome. I don't consider dinette seating to be comfortable. Truly comfortable seating is a small easy chair. Without a small easy chair I resort to laying on the Scamp's front couch, comfortable enough.
For some of us size and economics, of the trailer and tow vehicle, are a consideration.
Sometimes I think trailer volume is not enough. People keep going for '2 more feet' Escape
makes very nice trailers. Many with 17 foot Escapes went to 19 footers and now to 21 footers and I suspect in a year or two to 23 footers. This may be an opportunity for you because it has made the smaller Escapes available on the used market.
In closing, the Escapee club (nothing to do with Escape trailers) contains the largest number of fulltimers, present and former members approaching 150,000 couples and individuals. Most of these people choose larger rigs like small motorhomes and 5th wheels. We are Escapees and used to have a motorome but have down sized to a small fiberglass trailer for lots of reasons.
Good luck in your choice and wishing you many road years