You’re so right about treats and compensating for over-consumption. When I was diagnosed with T2, the advice I was given was…

1) Don’t try to live a 100% sugar-free life - it’s impossible to completely avoid sugar.
2) Eat all of the main food groups, but maintain a balance - the ‘Eatwell Plate’ shows the recommended proportions… The Eatwell Plate
3) A little of what you fancy does you good - occasional ‘treats’, such as a small slice of cake, or a biscuit, are absolutely fine in moderation. I became TMWCEOOB (The Man Who Can Eat Only One Biscuit)!
4) If you overdo it one day, pull back a bit the next day - it’s all about long-term balance.

I test each morning before eating or drinking, if I’m running a bit high I take it easy with my carb consumption that day. It’s worked for me for the past 15 years.