I use these. 29 gal Rubbermaid storage container, only mine is clear not blue like the one in the pix. I don't cut the sides down on them as I have cats that stand on their tiptoes when they pee. Given the ages/health of my cats, they have no problem getting in/out of the boxes.

I use Dr. Elsey's Cat Attract litter but that is a sort of clay based litter. Does the cat have an allergy to clay that you're switching to pine?