I personally don't like anything else in my systems besides the plant and hydroton. I germinate in coco and transplant into hydroton when ready. The coco washes off the roots easily. If you're not careful cubes can have a tendency to hold too much water and then develop algae and/or mold. Generally that is not going to hurt the plants except if they are young with few roots and the cubes stay saturated you can suffocate them stunting growth and possibly causing some root rot. But keep in mind when that happens it's user error. They can be used with no problems if you know what you are doing. I wouldn't use any kind of foam for cushions and whatnot. You have no idea what it's treated with.

I am having pretty good results with the 1" rockwool cubes. I have grown various lettuce types with them in 2" net cups and they work great. I fill in the gaps with Hydroton.

I use generic open cell grout sponges. I get sponges for $ .10 each from my tile friend who buys bulk but can also use car wash sponges from the dollar store. I get to choose the size i cut them into and they dont retain a ton of water like rockwool. I've never had issues with treatment on them but have heard others say they had an odd/chlorine smell. I always rinse them while squeezing them then soak in light nutrient solution overnight.

I have been starting in a small inside greenhouse under lights filled with vermiculite. Once they have gotten to a size I think will transplant well I take them and place them in either Rockwool or in a larger Peat pellet and put it into my NFT rail system. Once they are about 4 inches tall and hardened off I place them in the greenhouse outside which is dutch buckets.