First of all, I would do a bit of research and look at reviews of any saddle or brand you are thinking of trying. What suits some doesn't suit another, and there will always be conflicting advice given on this subject.
Another one for you to look at would be Symonds saddles. Whilst they are not eye wateringly expensive new, they are available second-hand. A lot of companies, such as Sheepham Saddles and The Saddle Bank offer a trial period on all of their saddles in stock (and there are quite a few brands).
There are saddles made on a shorter panel for short backed equines. Likewise, Velcro knee rolls and blocks offer adjustability for different riders to position them where they are needed in order to ride effectively.
Adjustable saddles suit some horses, but it is only the head plate that is adjustable - it does not take into account the rest of the saddle fit.
Finding a good saddle fitter is another minefield. There are SMS qualified fitters who have the 'official certificate' and those who have been fitting for many years and have the experience, but no 'official' qualification. Likewise, some saddle companies offer training courses to fit saddles - usually consisting or one or two days before they are deemed qualified.
Buying a saddle is not cheap, so please do your research beforehand.