We do something similar, although it's on a rock bed. We used 3/4" plywood sheets to cover the rocks, then used a thin wafer board type material to make strips to cover all of the plywood seams and where the corners meet up. Then we used the bottom of an old 18' easy set pool as our tarp material over the plywood (great use for an old pool btw!). This year we have the smoothest pool bottom that we've ever had. You'll want to make sure that your plywood extends out beyond the legs of your pool far enough to prevent the legs from sinking (or breaking off the edge of the plywood)- if you have a frame pool.

We went with a rock base, because we also take down our pool each fall, and for 8-9 months of the year we would have a mud pit in the yard. With the rock area, we put a fire pit and chairs in it for the other 8-9 months and avoid the pit of mud all winter. Just an idea if you have an area of your yard you could use instead of taking up your driveway.

With the mulch, I would be concerned about the water making a "tea" and really staining your driveway (if it is concrete).