In my opinion a scratching post no matter how good or how many will not prevent them from scratching your furniture. Cat scratcher furniture because you know they don’t want you to. That’s how they roll. LOL I recently saw something pretty awesome it was how to make a cat tower all DIY. I think what they used cost probably less than $15 and it was a good size cat towers and they usually cost over hundred dollars. But my cats love the cat towers. There’s things for them to crawl inside And they can scratch the sides like a scratching post and you can even hang things from them for them to swat around
My cats only scratch the furniture if they want my attention for something. If they want us to get out of bed first they will try a few scratches on the bedroom chair, and if that doesn't work they will scratch the corner of the mattress by my feet.
