I have always found the cheapest way to get insurance is through my bank account. Nationwide flex plus is the one i use £10 a month covers me and the other half, and I believe if you have children they are covered too, worldwide including my type 1. When i factor in that we both get brake down cover and mobile insurance as well its good for us. Before this i was paying upwards on £70 a year just for my own travel insurance
Some insurers charge a fee around £20 to complete a health questionnaire if you have a chronic disease. As this has been more prevalent in recent years I've taken out annual policies so the fee is only applied once a year.
I recently required a short 4 day insurance for a trip to Europe and was quoted on line a fee of £6.90. Once I'd called the insurer coverwise (usingAXA Ins)and been through the obligatory health questionnaire - no never been hospitalised, yes diabetes is well managed etc the fee went up to £25!!
I let them know the quote I'd had online was significantly cheaper and was advised that they could not do this over the phone but online you can opt out of cover for your condition which then reduced the insurance back to £6.90!
I've only tried a specialist diabetic insurer once and their charges were far higher than any others I'd encountered. Just my experience but I'd say always shop around for best deals and if taking more than one trip consider annual insurance as it tends to work out cheaper. Good luck.