Hard/Too High couch cushions

You have some good ideas. You can slice the foam with an electric knife, but I guess your covers wouldn't fit then. If you have a Joann Fabric Store, watch the ads for sales. I redid my kitchen chairs when they had a sale of 75% off of foam.

The source of the problem is that the foam is too dense, causing it to be too firm. Cutting plugs into the foam will not change the density of the foam. While the holes will enable the foam to be pushed into the empty spots when sat on, they may result moreso in creating a bumpy surface that might not wear evenly.

I would suggest removing the foam pieces fully, and slice a section off, the same way as slicing uncut bread. In fact, an electic knife works very well for cutting foam in straight sharp lines. Measure, and keep marking on the foam with a Sharpie marker if you want an additional cutting aid.

This is a 2 person job- one to hold the foam, the other to slice. Do not try it with scissors; they are difficult to work with, and will just hack up the foam.

Reducing the thickness of the piece of foam in this way across the entire piece will of course result in the covers not fitting exactly as tight as before. Without seeing a picture of how the covers are presently sewn, I can't say either way whether how easily they could be taken in.

You can buy a 3" camping foam pad in various softness at many home stores for around $13 that will be big enough for a full size couch. Sure made mine very comfy. You can also turn the sofa up on end and see if your legs just screw out, most do. Replacement legs can be found on Amazon, Ace Hardware, and I've gotten several sets at thrift stores, but you can get them for around $3 ea.

I think cutting plugs out will leave you with one lumpy couch.

The camping foam that Sharon mentioned above is very nice for this problem. Sometimes you can even find it in 4”. Sounds like your cushions might be pretty thick.

Another option would be to buy 1 or 2” foam sheets and you could layer them, wrap them in rolled batting and then cover that with something like a gauze type fabric to hold them in place before sliding them back in the cover. This has worked great for me on some outside cushions that were quite big.

On the hunt for camping foam, and if I can't find it, I will try the 2" foam 3 layers thick. Great ideas, thanks

Stick some memory foam under the fabric on top. Like form a twin bed, memory foam mattress topper?