This is the good stuff. The link is to https://pianosupplies.com
, PW's sister site.
Or, your tech could order one for you, or a piano store. The travel of the adjustment mechanism is only about 4 inches (which is one reason for the bench's rock-solid steadiness), so you may need to order longer bench legs to get your 7-year-old high enough. If it comes to that, there are devices that bring the pedals within reach for a young child, but their legs grow awfully fast at that age. The bench's legs are easy to change out with a socket wrench, and every five years or so, you might want to take the wrench and verify that the nuts are snug.
I have not found the maintenance burdensome. And, once you've worn out the first new grand piano, you might ship the bench back to the factory for a refurb and new upholstery, and get started wearing out the second piano.
I spent a lot of money on lesser benches, before I "came to Jesus" and realized, that I had thrown the money I spent on them, to the winds. The Jansen Artist bench (naugahide top, not the leather) runs a bit over $800. They say it will last a lifetime, and I believe it. It will also make your piano look twice as expensive.
Your young Mozart is lucky he has you. I will hope he sticks with it long enough to absorb, at least, the basics of music reading, while his mind is youthful, plastic, and effortlessly retentive, and puzzles like this are fun. Or, he could be like me, and wait until he has to sweat blood to learn the same skills.
Far be it for me to suggest, or even to recommend, such a base technique as bribery, but I have heard from piano parents that it can seem cheap, compared to other inducements. Some parents' minds seem immediately to turn to military school, but I am thinking more of the healthy application of healthy, but delicious treats, in the education of a family dog.
And maybe that's a good place to let it rest.