Just a couple of comments that might help. First trying to buy used is likely to be difficult. There are tons of used trailers available but very few truck campers.
There is a world of difference in comfort between a small popup camper and a medium or larger sized hard sided camper. I have found several conveniences that are very important: a decent wet bath/toilet, a north-south queen sized bed, a generator and AC when needed. Since your wife has expressed interest I would not compromise on any of these.
Weight is going to be a big issue. You can help by eliminating any campers with slideouts. Even so the base wet weight is likely to be at least 2500-3000 or more pounds. On top of wet weight, we added two people, a generator, 2 solar panels, oversized batteries, tools, clothing, food, cooking gear. That bumped up the weight by more than 2000 pounds!
You are going to consider modifications for your truck. Hold downs are the least of the expense. I added supersprings to bring up the load handling. I don't know what you can do with rear coils. Yuck! You will need to upgrade shocks to Ranchos or equivalent. Tires are another serious consideration. My Dodge Ram came with 17 inch wheels. The highest load rating tire available is limited to 3200 pounds. After years and tens of thousands of miles driving overloaded, I bought wheels and 19.5 inch commercial tires from Rickson for close to $4K.
Finally, if you buy new, I highly recommend Northstar. Their campers are well built, well designed, tried and true. They don't have slides and are typically also a bit narrower than the maximum 8 feet.