I finally built my pallet bench! I used 5 half pallets I had saved: four for the seat and one for the back.
If you can tell, I found one half pallet that had its slats almost solid for the top of the seat. I plan to buy or make cushions for it but until then this makes it perfectly comfortable for sitting. I stood the back pallet up to decide where to add the supports. Once I determined this, I made sure my pallets were square and where I wanted them. I used the spare pieces from boards I cut for my garden frames. I used two screws on the top and bottom of each support and used one screw in each middle pallet. This kept everything from shifting around.
For the arm rests, I used more spare pieces from the garden frame. The front support was an added benefit because it further added to making the base more solid. I put them on at an angle to accent and better fit the angle of the cross piece. Last, I screwed on the cross pieces: one screw in the back and two at the front (where the hand would rest).
For not being much, I think it turned out great. I’m really happy with how comfortable it is. Now, I just need to paint it and it will be ready for the garden.