I'm going to assume your truck is 4wd. You only need a leveling kit in order to fit 35's. There are two different options, leveling spacers or adjustable struts. Spacers are quite a bit cheaper. You can get Hell Bent Steel ones for around $80. However the better way to level the new Rams is the Bilstein 5100 adjustable struts. They have different height settings from 0-2.8". That would be the best option of you are fine with spending a little more money.
If you are sticking with the stock wheels to mount your 35's on you will need 1/4" spacers. If you go with aftermarket wheels you need 20x9 0 or -12 offset or 20x10 -12 or -24 offset. The more of a negative offset you go with gives you a greater chance of rubbing on the inner fender when you only have a leveling kit.
There are tons of threads and posts about leveling and wheel/tire set ups in the Lifted 4x4 section of the forum HERE
. I'd suggest you take a look through a bunch of those, you'll learn quite a bit.
My signature also has a link to my wheel and tire install thread if you want to take a look. I'm running a 2.5" HBS level with 20x9 -12 offset wheels and 35x12.5 Toyo MT's.