Hello and welcome over on this forum, though I'm sorry for the diagnosis. Just remember Kea doesn't know he's any different. But now you have an explanation for his higher dose and a path forward.
First and most important, will be getting him to a dose where he's seeing better numbers, mostly under renal threshold. It will be beneficial if you can follow Tight Regulation for dosing, which should be easier with a Libre on him. At some point you may want to consider a switch to Levemir. It is similar action to Lantus, but onset and nadir are a couple hours later. The big thing is that Lantus has an acid base that can sting at higher doses.
If you didn't see anything below 200 today, you can increase to 7.5 units now.
As for treatments, can you tell me where you live? Surgery and SRT aren't available everywhere - travel has been a deciding factor for some people. As does cost. Surgery is over $10,000, as an example. Though some people here got it done when there was a donation in place at AMC to help. In England, surgery is usually the treatment of choice.