Just a word of warning about travel insurance through Columbus or any other insurer that doesn't specialise in insurance for people with long-term and/or chronic conditions. All insurance companies will offer to insure you - but most will exclude any existing medical conditions. For someone with a medical condition this makes the insurance pretty much useless because, if you were to have a claim, the insurer will just claim that you are not covered for whatever the problem is because of your pre-existing condition.
When getting insurance quotes it is vital to ask them to confirm that the cover they are offering does include existing conditions that you have advised them of.
Edited by Dennis: the above is not intended as a criticism of Columbus - they may or may not cover pre-existing conditions, but as a general rule of thumb, the cheaper the premium then the less likely that the policy will cover your diabetes.