All I can say that you must make this trip. It's unforgettable. I was in Palma last week and the train is still running. I don't know if it stops later in the year for a winter break.
We did it a couple of years ago from Soller to Palma & back later in the day. Great fun/ stunning scenery and a trip back in time.
I'm sure there must be a web site with more info. in fact here you are!!

http://www.sollernet.com/trendesoller/en2.html

THANKS FOR THE INFO ,JUST NEED TO FIND OUT THE COST

It cost 11€ return last year, the train runs throughout the year and stops for the view over Soller on the tourist train. It is well worth while taking the tram down to the port when you arrive in Soller 3€ each way.

Enjoy, good luck,

Dave.

What are the seats on the train like for someone with a bad back ?

Some wooden slatted, others simular to bus seats where you can move the back rest to face the way you are travelling.