Check your door jamb sticker for the trucks CCC.
Work back from there subtracting things like passengers, camp gear, etc that will go in the truck.
That number is how much you have left for TW.
Once you have that number you can then start to look at floor plans that have a TW thats lower than that number. You'll need to also realize that brochure weights are typically lower than shipped weights.
So if you find a TT with a TW of say 500 lbs you'll need to add 300 lbs to it because 1st it's an advertised low weight and you'll also be adding things like propane, battery, stuff under the bed and in the front storage compartment, along with a 100 lbs for a hitch.
Now that you've guesstimated your TW, you can google up RV trailer MFG's and start looking on MFG web sites for rear living style trailers.
A good rule of thumb for newbies is to take 12% of the TT's GVWR and use that as your TW. That will provide you with a decent margin.