Good morning, Irene, and welcome to the most awesome place you wish never had to find!
Hometesting is indeed a most valuable resource. While insulins like Prozinc and Lantus ARE long-lasting and more gentle, cats can still have WIDE variances of numbers on them and can still go hypoglycemic on them. Hometesting regularly will help you ensure that Themba is always safe, AND will allow you to take control of Themba's dosing so that you won't have to rely on the vet.
I highly recommend the Relion Confirm meter from Walmart. The meter is only $9, and strips are 50 for $20, which is the best retail price you'll find. The Arkray Glucocard 01 is the generic version of the meter, and you can get strips for even cheaper at
ADW. You'll want to use a lancet that is 30 gauge or larger (the smaller the number, the bigger the needle) at first. You'll also want to get a low carb treat to give with every ear poke, successful or not. You'll find that soon, Themba may be begging to be tested because he wants a treat! We use Purebites freeze dried chicken breast, though I buy the big bags in the dog treat aisle as they last longer and are more economical.
Before you get started on Lantus, I'd encourage you to head over to our Lantus forum where we have a number of stickies with invaluable information on how lantus works, the protocol many of us follow, etc. I suggest printing them out and keeping them in a binder with the contact information, location, and directions if needed to your closest 24 hour vet. When I was first starting out, I'd need a particular piece of information in a hurry and would have trouble trying to remember which sticky I saw it in. I found it was much easier to have them all printed out, where I could take notes and mark them up however I saw fit. You'll find many of us post a daily thread or "condo" over there. It is truly a wonderful family. You'll want to use our spreadsheet template to set up a method of tracking Themba's BG#s. It is an invaluable resource.
Also, you'll want to make sure you have the correct syringes when you make the switch. While prozinc is a U40 insulin, lantus is a U100, so the syringes are different. Walmart is also a good source for syringes... a box of U100 syringes is around $12 for 100... much cheaper than the BDs! I'd recommend getting the short needle ones.
Ask for these: 3/10cc, 5/16", 31 gauge (or 30 if that's all they have). They should have the units marked in 1/2u increments, which is important. Generally, you'll be making changes to the dose in 0.25u increments, which are MUCH easier to measure on the 1/2u marked syringes.
What food are you currently feeding? That may be having an effect on the numbers Themba is showing on the Prozinc.
Please ask questions as you have them... you'll find that the folks here are more than happy to help!