I hate to say this, but since bones in the diet can cause constipation, changing the diet should be the first, most important thing you do. If you want to feed raw, feed meat only but no bones.
Psyllium can cause a deadly intestinal blockage, so I must warn you to be extremely careful with that. Also, too much fiber in the diet interferes with nutrient absorption, it prevents nutrients from the food to be absorbed.
Since constipation on a regular basis will stretch the colon to the point where neither a change of diet nor medications can be effective and removing the colon is the only option left for the cat, please think very, very carefully about the dietary issues and don't just follow recommendations that can have disastrous consequences for your cat.
Change the diet and work with foods instead of added fiber to soften the stools and make your cat regular. And do this before it's too late.
Constipation can become so serious that cats as young as two and three years old become candidates for the surgery. I don't want that to happen to your cat.