My experience is that local mattress makers have good quality and prices. You could certainly use wool. Latex is another question. Mattresses are thrown out all the time. Your best bet might be to take a relatively new mattress with good-quality metal springs and replace the materials with your preferred materials.

I don't know where you're based, OP, nor where Sigrid is, for that matter.

I live in New York City, where taking a thrown-out mattress is a good way to introduce a bedbug and/or cockroach infestation into your home—and the homes of all your neighbors, if you live in a multiple dwelling. That would neither save money nor be safe.

On the other hand, in NYC you can go to a foam supplier to get foam cut to whatever size and shape you like. You can wrap your foam in wool if you know where to get the wool (I don't, but there must be suppliers somewhere). I don't see the point, myself, but everyone's different, and your situation may be very different from mine.

Best of luck with your project.

SleepOnLatex has toppers in up to 3". I've used one and it has lasted 10 years. You can also look online for a Japanese domestic.made futon for around $300. You'll get better higher quality for your money check EMOOR and FULI. Private equity buyouts are the reason mattress prices are a rip-off. Ime. TFS uses latex core, cotton cover and wool fill in US made Japanese style futons.

My gandma from Europe used to make it using batting. Now people use new technology. There are a lot of tutorials on youtube people are doing it. Check out which one is appealing to you. And good luck with your project!

I am not affiliated with this company, but I love my mattresses from them. You can customize the layers and get a beautiful wool cover.

https://sleepez.com