Hi. T1 parent here also.
First thing to say is that it will get easier over time. It is extremely stressful for everyone, especially the child, at the beginning but in time you all learn to live with it, it becomes less frightening and more a way of life. The tech makes life so much easier but you need to learn the basics first.
Yes cheese, yoghurt, nuts, salami, cut up veg, berries etc.
But things that will let your child still feel like a kid and that they can still have treats are diet fizzy drinks, slushies (are usually diet but you can test them with a strip and monitor if in doubt), the small multi pack crisps that aren't potato that are corn based or like Skips are less than 10g, 2 finger Kit Kats are about 10g and generally any wafer based biscuits.
Watch their well-being over the first while and allowing them to enjoy meals and snacks without dinner being a major undertaking if you can.
Nobody understands just how hard it is unless they've been there so ignore all the well meaning advice and listen to your nurse/dietician/doc.
One thing I majorly regret is letting my son see my own anxiety, and standing there while I explained the diagnosis drama to friends etc. Not my finest moments.
But 5 years on he is completely fine, doesn't let it get in the way of anything he wants to do.