Concrete blocks aren't boring, they're just a good starting point for ideas! And nothing is quite as solid as concrete.
If you use concrete blocks though, you want to set things up so the washer can't vibrate itself off the blocks and fall over. What I'd do is find a way to fix the blocks to the floor, perhaps by drilling through them and bolting them down, and then fix the washer to the blocks, perhaps via a piece of plywood with a furring strip around top and bottom so everything stays where is should.
Another interesting possibility is to pour a 3" thick mesh-reinforced concrete pad on the floor, in the dimensions of the washer. If the pad is 3 feet square, it would be 9 cubic feet of concrete or a total of about 340 pounds in weight on your floor. That would be six 60-lb. sacks of quick-mix. Mix it stiff (as little water as possible) in an electric mixer (you can rent these inexpensively) and keep the finished slab damp for two weeks to assure it develops maximum strength as it hardens (concrete should be *cured* not *dried*).
Or you could build up a pad on the floor with multiple thicknesses of plywood, perhaps also to 3" depth, all screwed down with deck screws. Technically this becomes a "stretched-skin" surface, so it behaves with greater rigidity than might be inferred from the fact that it's made of wood.
Last but not least, all front-loaders like to vibrate because there is no way to automatically distribute the weight of the load perfectly evenly before a spin starts. Many front loaders have self-adjustment routines where they rotate a bit to distribute the load, then try to start spinning, and if they sense excessive vibration they slow down and try again. This can take a few minutes or more each time, which some people get impatient about, but after all the machine is fully automatic so you can just let it do its job and not worry about it.
You can minimize vibration through careful loading. Run full loads, and don't mix heavy and light materials e.g. towels and sheets in the same load.
Or if the whole house keeps vibrating, just lie down on the floor and enjoy a nice back massage!
