Have you tried Diabetes UK? They always have a partnership with an insurance company to provide travel insurance for people with diabetes.
I don't know the cost because my employer pays my annual travel insurance ... because I travel a lot for work, not because they are incredibly generous.
Interesting. I paid a lot more for an annual policy last year. Ironically I must be a much lower risk now than for many years before diagnosis because of all the improvements to health over the past year!
Best quote we had this year was from HolidaySafe, next best was EHICplus. These were for an annual EU only policy for two over 70s, one with T2D plus CVD.
I got quotes from the "specialist" insurers which were significantly more expensive than "standard" insurers. I went with Sainsburys bank as there was no extra charge for covering my diabetes (actually cost more to cover eldest child for ear issues).
We have used them a number of times and importantly they were really good when we had to make a claim.
Just make sure that you declare everything and double check policy is as expected before travel.