I am not familiar with diaonex. Is it an oral med that is supposed to take the place of insulin?
Treats - do you have a petsmart anywhere close by? They have a section of low carb cat treats, including one I use. It is made by beefeaters, and they are tubs of freeze-dried shrimp, salmon or turkey maybe? My Bob is a huge fan of shrimp.
You can also use real shrimp (boiled). The best treats are meat rather than vegetable based. Most store brand cat treats are veggie/grain based, and are higher in carbs.
Another thing you want to avoid if at all possible is any kind of dry kibble cat food. High carbs.
small pieces of turkey, chicken, lean beef. I think all of those (as long as they are just plain, no seasoning) can be used for treats as well.
Wellness (also from petsmart) sells low carb meat treats.
I learned to shoot Bob in the scruff too, but didn't have trouble from him about it. I just scruffed him with my left hand, used my forefinger and thumb to make a little tent, and stuck the needle into the tented skin/fur. As long as you make sure the syringe is parallel to the body, so you won't hit any resistance other than the skin going in, it shouldn't hurt much. One thing that may cause discomfort is if the insulin is cold. After you draw up the insulin into the syringe, try gently rolling it in your hands to warm it up a little before shooting. Some people actually shoot while kitty is eating and is distracted with that, and the kitty doesn't even notice the shot.
I never had to "numb" Bob, so I'm not sure how to go about that. I think you want the area where you're shooting to stay dry an not have any ointment there, because after you shoot, you should rub that spot a bit to make sure the insulin actually went inside. If it's wet after shooting, that means you had a "fur shot" and not all the insulin made it into Jimmy. In that case you would never "try again", because you wouldn't know how much went in or didn't go in. But it would affect how effective the dose was over the next 12 hours.
I fully understand your feeling of being overwhelmed. There isn't a person here who hasn't felt just like you do right now. But all of us got past that stage, and everyone will tell you this (and it's 100% true)... this will get easier, and Jimmy will get better. It may take a while. While some cats can improve rapidly, some take a long time. You'll hear this a lot too - ECID. Every Cat Is Different. You can do this. We all can help. There will be more folks along to welcome and advise you. You just picked a "slow" part of the day to start your journey!
Keep you chin up. And take deep breaths.
Carl in SC