If you are reasonably handy, any reasonable power amp will do - the B&O one is called a MCL2P and is available second hand. You could also use something like a Quad 405 power amplifier which Graham, another moderator favours for good reason.
LifestyleAV if you are in the UK offers a good range of used Beolab speakers - I favour Beolab 4000s for sound quality at a reasonable price.
In your case, I would consider using your Bose speakers with a cheap power amplifier until you can afford to upgrade - if that is what you have!