How to use a saddle?

English is different so I can't really answer Western tack questions.

If you've ridden the trails and can't get comfortable you might need to try out other saddles and see if there's something better for you.  It sort of drives me crazy when people start talking about "correct".  I have a dear friend who does that.  "I'll never show but I want ride correctly"  Okay, toots, if all you're doing is hacking along the trail then who gives a hoot if your wrists are broken and you sometimes slouch?  You're out to have fun and not worry about that.  Are you in an Australian?  Was that you who was thinking about the Cashel?  My Australian is quite hard on the seat and needs a foam pad - which Cashel also makes, btw.  Your feet need to be in a position so they can't slip through the stirrups if you fall off.  That's the point of that.  All safety rules should be followed imo.  Make sure your stirrups are long enough or you won't be comfortable.  There's my 2cents!  []

I was taught to use the balls of my feet.
 
For sitting, in a western saddle, try to sit on your pant pockets, even tuck your butt under.  You want to sit on your SEAT bones, which are your PELVIC bones between your legs.  Lift up your belly button if you can.  Your legs should be RELAXED, never out in front of you.  Do not lock your knees or brace yourself against the stirrups.

I would say if you absolutely have not found a comfortable position in your saddle by now, then you probably need a new saddle.  Like Hunter said, if you're riding down the trail there really is no need to sweat riding in the "proper" position.  Some will argue that it makes your cues to your horse clearer, but really how often do you do anything that requires the same level of finesse as you would use in the show ring? 

When I ride in my western saddle I prefer to ride with stirrups a bit on the shorter side.  This helps me keep my weight in my heels better.  I put the ball of my feet in the center of the stirrup tred, maybe a tad forward, and I sit on my jeans pockets.  I do try to keep a line from ear to hip to ankle.  Everyone is different, and every saddle is different too.

Consider changing your stirrups to endurance ones. They are great for trail riding. I use to have the same "ball of the foot" pain, but not with endurance stirrups!

I have a barrel saddle that I use for riding green horses. (it holds me in just in case) I use it as an extra saddle if someone is using my other saddles. I can not trail ride comfortably in it. If you plan to mostly trail ride. I would investigate getting a different saddle.