If you can't test, for whatever reason... I'd say just go keto. You shouldn't see any spikes on that, really. If you can't test to check foods, then just go for foods that don't spike one at all. For me, if something makes me spike (and it would have to be 3.0mmol/l higher than where I started from or more, for me to feel it) I get a little confused, palpitations, wobbly legs, hot flashes, basically the same thing that used to happen at hypo's. If you remainhigh for a longer period of time, your body gets used to it and you won't feel a thing. I never noticed hitting 22.0mmol's for instance, pre-diagnosis. That was my "normal". But if you want to avoid feeling like that all together... Just go seriously, very, very low carb with a ketogenic diet (Or carnivore? Even less carbs in that than keto).
Good luck!
Jo