MMM or not? This will make a difference, as with a MMM you cannot add much width with a BX. In my case 1.25 inches was the max.
On a little BX, no need to buy expensive spacers. what you can find on Amazon or Ebay will work fine.
There are threads here and at TBN regarding the subject, with links to cheap spacers that work perfectly on the BX. Maybe you can find such links, or if I do I will post a link...