Most people tolerate psyllium fine, but it caused a lot of gas for me and increased my frequency by quite a bit. It did thicken my stool though. I had better luck with Citrucel (methylcellulose). It did not cause gas or increase my frequency, other than the extra bulk it caused. I didn't stick with that either because I didn't feel it improved my function enough to be worth the bother.
I am not sure there is any particular fiber supplement you SHOULD be using. Just experiment and see what suits you.
Jan