I have worked with the custom braces before. Generally when a Dr. says " custom brace" they are not referring to a "ace bandage type" but more of a "metal hinged strap on with velcro type" . If your knee is " shot" I doubt an "ace" will benefit u much. While a custom brace is expensive ( insurance/medicare will normally cover about 50%) they do offer alot more support than a common ace/stretchy one " will. Your knee maybe beyond even a custom brace ..... braces can only do so much. ( custom brace DO come in pretty colors/designs-- but of course they cost more)
If your knee is to the point of " bone on bone" It maybe time to bite the bullet and get a knee replacement. New technology and designs have come along way at improving knee /joint replacement.
Good luck