Welcome to FDMB
Tim & Pookey is right, instincts are our best friend, the best insulins for cats are Lantus and ProZinc, they are a 12-hour insulin gentle on the cats' system, also home testing is a priority, judging by Théo’s physical presentation, is insane, cats hide illnesses very very well, and hypoglycemia is not a pretty site aside from the fact that it puts at risk your cat's health and heart, even death, You can purchase as Tim said the ReliOn Premier monitor and strips (Walmart) the meter is $9.00 and the strips are $9.00 for 50 or $17.88 for 100, is always good to have extra strips handy. you do not need a Pet meter, any human meter is just as accurate; so, Testing before each shot is very important to avoid hypoglycemia, you should request your vet to prescribed Lantus or ProZinc, it is your cat, you are in control, you want what is best for your cat, also if your vet speaks about doing a curve on Theo, this can be done at home, is simply testing every 3-4 hours for a cycle (12 hours) cats are very sensitive to stress, what better way to stress Theo than a vet visit for a whole day inside a cage, so the curve glucose levels done at the vet will be unrealistic, high, this can cause an unnecessary dose increase.
There's is also the option of the CGM , continuous monitoring by ABBOTT, link below
Diabetic cats need to have a diet of wet can or raw foods between 0-10% carbs, should be on a feeding schedule with 3-4 small meals or snacks during the day to keep the insulin in check, besides the two main meals before each shot. Link for a Drs approved food list below the third column contains the carb %, we look for Dry matter Carbs, do not feed any diabetic food or "prescribed" food they contain between 18-30% carbs, cats cannot digest carbs. so no kibbles, no grazing
We are very numbers oriented, we would love to help you stabilize Theo, we would like you to create your signature and Theo's spreadsheet this way we can all be on the same page6, keep posting we are here for you. if you have difficulty creating the SS let us know we would be more than happy to create it for you, there are sticky notes in our Main Menu that have much valuable information, and it does gets easier!
Sticky - New? How You Can Help Us Help You!
https://felinediabetes.com/FDMB/threads/how-to-create-a-spreadsheet.241706/
Info - Dr. Pierson - new Food Chart
Getting Started With Continuous Glucose Monitors (CGMs) for Diabetic Cats