Welcome to FDMB.
Recommended insulins are Lantus, Levemir, ProZinc, and BCP PZI. Some cats do OK on Vetsulin/Caninsulin; in others it may not last a full 12 hours, requiring more frequent dosing.
For the safety of your cat, we advocate home glucose testing with an inexpensive human glucometer such as the Target Up and Up or Walmart Confirm or Prime. You'll need the matching test strips, plus lancets labelled for alternate site testing (25-28 gauge).
There are numerous over the counter, low carb, canned, foods which may be used rather than expensive RX foods which are no better, and are sometimes worse, for diabetic cats. See Cat Info for more info on this. You must be home testing to change the food while on insulin, as changes in carbohydrate level significantly impact the insulin required.
See my signature link Secondary Monitoring Tools for some other assessments you can make to evaluate your cat.
Hi there and Welcome; you will find a wealth of information here. As BJM told you above the low carb wet food you will want to feed your cat. The carbs should be 10% or lower. When you switch to low carb from higher carb food, the Blood Glucose (BG) can drop as much as 100 points so it is really important that you home monitor. Here is a couple links of how to test using your cats' ear. If you need any help please ask. We are here to help.
Hi Jo and Bob, welcome! The injections are not so scary, try not to worry too much - you'll be fine Hopefully the vet will show you how to home test as well, if not, there are a ton of videos on that too and I see Bobbie has already posted those links. Good luck, let us know how you go today!