Start with checking out this gallery for the different setup tire size and offset.
I'll be going 10" wide with a -18 offset which will have wheels sit slightly outside of the wheel wells.
It will depend if you go 9 or 10" wide what offset you will want. The smaller the negative offset or higher the positive offset will push the wheel into the wheel well.
Custom Offset
If you don't want rear spacers, look at Clayton Gladiator rear coils 2.5 or 3.5 and research how much lift you will actually get. Many run them on here. I'm also not sure about the towing with them, so research.