Absolutely 3/4 ton, and get a diesel. Since you are buying used, absolutely under no circumstances get a 6.0 Powerstroke. I’m not familiar with the newer ones but these are junk. Duramax or Cummins is fine but the 6.0PS will be in the shop more than on the road.
It’s been several years back now, but my dad pulled a trailer 5-6 days a week all year long for work as a contractor. It was a 7x12 enclosed trailer at an estimated 6-8k (never weighed it). Originally he pulled it with a 99 Silverado 1500 2wd reg cab short bed 4.3 v6. It did the job, but it was obvious you needed more truck. Squatted the rear end quite a bit, nowhere near enough braking power, and it was enough of a strain that I don’t think it would have lasted long term. Did that for 4 years/80k miles, finally was able to get a Duramax, 2004 2500 crew cab short bed 4wd. It did a much better job at it. It was an appropriate truck for that load.
If you are only looking at 3-4 years old, you likely won’t save that much over a brand new, left over stock from last year when you buy. Full sized trucks in general and especially diesel pickups hold their value very well even in a non-COVID-19 market.