I agree with physio about bracing your ankle up - its like painkillers, ok as a temporary solution but you end up doing yourself more damage in the long run. He's right about re-educating your ankle as well - it was a good 2-3 years before I was fully recovered from a torn achilles tendon and a lot of that was spent learning to walk without a limp.
If you're after protection from knocks etc. you ought to be able to find ankle guards for football in a sports shop - failing that, invest in some expensive football shinpads as these often have them built in.
oh - and learn to roll when you hit the ground. A good crash should see you 15-20 feet from your bike when everything stops moving