IMO, much of the current “saddlery” business is a scam. “Certified fitters” got their accreditation from an internet course, and don’t have a clue, and don’t ride adequately themselves, so why would they have a clue? I’ve seen them “pontificating” about what is necessary for a client, I find it hard not to laugh out loud. Modern saddles are often crap that fall apart in a few years, that are often impossible to ride well in, and often don’t fit well. Buyers think that the more they spend, the better the new saddle will be. That’s not true. Be careful who you take advice from.
If you have a horse who has some damaged or misshaped back, some complete oddity that makes a regular saddle not fit him well, you might need a custom saddle for him. Don’t go and buy such a horse on purpose. Buy a well conformed horse, suitable to be ridden, with a good back.
Saddles come in several different widths, and have various shapes. Find one that fits your horse, and that you find comfortable- that you feel allows you to ride to your maximum ability. Buy that one.
Older saddles can be restuffed if necessary. Billets can be replaced. Older saddles were built to last, not to break or wear out- they were built when quality workmanship was a thing. Unlike much of what is available these days. Brilliant riders in decades past rode very well in these saddles. May current riders ride as well as those riders did (often, they don’t).
The issues that are often involved in saddlery issues, as long as the basic fit is adequate are 1) The length of the riding sessions- if you ride for 10 hours at a time, endurance riding or working on a ranch herding cows all day, slight saddle fitting issues may become a problem. 2) Unbalanced rider, sloppy riding. 3) Rider weight- more issues if you weigh 300 lbs. 4) More padding, deeper seats, blocks, rolls will not make you ride better or be more secure in the saddle. The most secure saddle is one that allows you to stay as close to the body of the horse as possible. Less is more. Anyone who tells you different is just trying to sell you a saddle, and probably an expensive one. Be skeptical.
Good luck saddle shopping. It doesn’t have to be expensive.