Most of us in the states with winters start thinking about saddle fit in early Spring. Not a bad thought... the saddle probably needs a little tune-up and the weather is tugging at us to start thinking about Summer! Here's food for thought though. At least once in your horse's show career, think about having your saddle evaluated at the end of show season. Why?
At the end of a show season, your horse is usually in the best shape of the year. You have been training and showing for a few months and you are both probably pretty buff. If you purchased this saddle when the horse was not quite at peak performance, you may want to ensure that this saddle still fits well and has room for the muscles that have developed. A quick tweak of the wool or perhaps a different padding system might be discussed so that there is no discomfort. As the colder season approaches and you begin riding a little less you can fill in with a thicker pad when your horses muscles begin to settle into winter.
Have the confidence that your saddle, at your horse's peak condition, is appropriate by having it checked just after the shows end.