If you're looking to live in your truck, I would be looking to get something taller than the Leer 122 you mentioned. Any extra height is worth a lot when you are treating the truck bed as a home. I don't know how much you'd be looking to pay for a new 122 in your area, but new toppers are pretty expensive around here. Anything good is well north of $1500, with the taller ones running about $1800-2000 when I last looked. I ended up getting an ARE D.C.U. It was about 2500 in the configuration I got. Double rear swing-out doors (so, no tailgate) with windows, opening side windows, ladder rack on top. They come in different heights, and are completely customizable. Might be worth looking. I know you can get them cheaper than what I paid; just depends on what you want.
Also, and I know you know this, but it's gonna be hard to keep dog hair off of every piece of clothing you have if you are living with your bud in the back of the truck. Might look at coming up with clothing storage in the extended cab portion of the truck. Maybe you said that earlier, though, and I just missed it.
As for curtains, I had the local gear/clothing repair lady cut/sew some curtains for me, using a single, large light-blocking curtain for the fabric. Cost me 10 bucks or so at Walmart, and another 30 or 40 to get her to cut/sew. I placed grommets in the curtains, and I hang them on little 3m folding hooks that I've stuck up inside the shell using the heavy-duty 3m double-side adhesive foam. Works like a charm. Put 'em up, take 'em down. No problems. I went with a completely removable curtain assembly because I use my truck to haul rescue dogs from the rez to accepting shelters frequently, and I have to be able to power-wash the inside of the bed/shell each time, and then bleach it down. I couldn't have curtains in there all the time.
Please take all my comments with a grain of salt, and with the understanding that I do not live in my truck. I use it to sometimes sleep in after work (instead of making the 80-mile one-way commute), and to haul dogs and wood and bicycles and whatever else.
here is my shell, shortly after I bought it.