I would use dimensional lumber. Once you have weight on 'em, let the car settle for a minute.

I replaced my Sears jack, worked well for years , with an aluminium HF unit. It has two pistons, one of which needed persuasion to release, has, so far so good, but won't buy one again.

I have two jack stands that came with the Sears unit and have purchased another pair. One set is taller than the other, oh well.

I use a chunk of 4x4 on the pad to both raise the lift and to be nice to the car.

No pics. Just imagine a ham sandwich:

Bottom piece of bread is the jackstand, the ham in the middle is the plywood, upper piece of bread is the cars jack point. Yummy :D

I like 3/4" ply wood. Ply wood takes the guess work out of what type of solid wood to use, grain, whether it's going to split on you or not.

Ok that helps. 3/4 is thick but perhaps necessary depending upon the profile of the jack stand. I was thinking thinner, but it also may split or something.

I bought the Arcan Hybrid floor jack at Costco. The best jack I've used. Totally smooth to release, no sudden drop, and quick to raise, 3.5 pumps and it's at full rise. Well built, by far worth more than the $99 price.