Idaho and the Northwest have a plethora of used truck campers and some dealers.
I would say go look at several different units.
3 people is nothing for either a long bed or a shortbed camper.
I sleep 2 adults, and 4 kiddos in mine, but my kiddos are small.
No slide either. You have to make a plan, look at floorplans, spend a lot of time in Craigslist if you are buying used. Look at tons of pictures.
If you're buying used, you can buy something reasonably priced, try it out and see what works for you.
If you find that it is less than ideal, assuming you can ever find an ideal camper, you can always put it up on Craigslist.
Best of luck.