This is a timely question - I just had an appointment last night with my obgyn, and we discussed getting me off of estrogen-containing oral contraceptive since I have type 1 diabetes and a history of migraines/auras (15 years ago but apparently this is still a risk?). I am hesitant to switch to something different, since the one time I switched to a different pill than what I've taken for a long time, my blood sugars were icky for a month, but this one time episode is probably a silly reason not to consider trying other things.
She recommended a progesterone-only method with my history of migranes with aura combined with diabetes, which can be the progesterone-only "mini pill" (an oral pill), Depo Provera (injection every 3 months), Implanon (I think the brand name is Nexplanon actually, and this is the small implanted capsule put in your upper inner arm), and Mirena and Skyla IUDs. There is also the copper IUD (Paragard) which has no hormones at all. I'd say overall, she was open to me trying any of these options, but here are the "general" observations she said she observes with her patients with each option:
Progesterone only pill has to be taken very accurately every day, and its a higher dose of hormone since it is taken orally and needs to be systemic to reach the organ it needs to.
Depo Provera she said is great, but you have to go in every 3 months for an injection. A very small fraction of women have significant weight gain, and many have some spotting as they start on it.
She was very positive about the implanted capsule (Nexplanon, Implanon) and said women really have no issues with the placement, and she'll get some women who get no period on it, and some women who vary with spotting or normal periods. She said the higher number of women whose period doesn't go away is the reason some women shy away from this method (vs IUD, which causes no period at all in a pretty high fraction of her patients).
And the IUD, which is the last option. She said Skyla and Mirena are about the same (one lasts 3 yrs vs 5 years), and many women get spotting for the first few months then no period at all and rarely can feel the actual device in place. Paraguard is the non-hormone copper IUD, which will result in a period each month that is just like if you weren't taking birth control.
Basically, both my obgyn and my endocrinologist said they can't think of any of their type 1 diabetic patients that have complained about a specific type of birth control affecting blood sugars - I definitely asked this question because this is always my priority when making a medical decision! I agree with you - looking online, you mostly see horror stories, and not the stories of women who absolutely love their birth control method! But everyone is different, and when it comes down to it, I think you've made a great choice and you'll have to give it a try knowing that if you get the implant and for whatever reason it negatively affects your health or diabetes, all you have to do is get it removed and try another option (they don't HAVE to stay in place for 5 years if you're unhappy). Good luck!