I like the idea of the small truck camper + trailer. The trailer will be much better for living and working in.
Go used on the truck, small + used on the truck camper, and moderate size on the trailer. On the trailer, you want a dinette for a place to work, and another place to sit, so you can relax away from your work space.
Your leisure spot doesn't have to be a sofa, it could be a recliner. A lot of floor plans have a bedroom divider wall with sofa on it, then dinette, a mid-kitchen, rear bath. You could replace that sofa with a comfy recliner.
You could start out with the truck camper, and take your time looking for the trailer. If you winter in AZ, there are lots of trailers of all types for sale there.