The crew cab and diesel will be eating into the available payload you have, so as suggested above I recommend you get the truck weighed and work out what payload you have to play with, then when you look at campers (even if you just start looking on-line) you can see what their weight is and compare to your payload. bear in mind that if the manufacturer lists the 'dry weight' then you will need to add a lot of weight to that for water, food, gear, accessories, etc.
Of course, it might be that the campers you see that are acceptable from a weight perspective are not what you want, meaning a truck upgrade. In that case you probably need to think carefully about your needs when camping. In fact you should probably do that anyway. Do you want something large, spacious and luxurious?, something compact and rugged you can get out into the back woods with?, something in between?, how many people will sleep in it?, what sort of climates will you be camping in?, What do you want to take with you (e.g. kayaks, motorbike and so on)?, would you prefer to move on each night or two, or would you prefer to park it up for a week in one place?, etc. If you get a clear picture of the sort of use you will put the camper to then it will really help your choice.
Steve.