Maybe you should look at the journey as well as destination. in view of your back problem. Easiest route to Bruges by train is via Brussels where you change trains in the same station. The slightly shorter alternative is to change at Lille (stations as well as trains) and then again at Kortrick. I suspect the latter route is out of the question so you will be going to Brussels, in which case you may feel like staying there. If it wasn't for your back I'd recommend using Ghent as a base (changing at Lille) and you could visit Bruges and Brussels in easy trips. In my (humble) opinion Ghent is nicer than the other two!