You may be able to make another 5.5ft bed camper shell fit, but I'd stick with a Titan one. I'm hunting for a specific type of camper shell myself, so I look through nationwide classifieds daily. There are plenty of them out there. Try using searchtempest, or adhuntr.
If you simply want a camper shell to cover your bed and don't plan on carrying any significant loads up top, any type will do. I personally am partial to A.R.E. because of their hidden, heavy duty hinges. Snugtop and Leer are the other big players, with Leer being nationwide and Snugtop being very popular out west. There are also Ranch, Jason, and a few other brands, but they are typically considered lower quality than the big 3 (but they are a fair bit cheaper).
As a starting point I'd recommend you check out the Leer and A.R.E. websites. Punch in your year/make/model and go from there so you can see what you like. After that, shop the used market accordingly.