Hi Claire, I think I know exactly what you are going through. When I was diagnosed I ended up in hospital for the first 24 hours whilst an insulin drip brought my glucose levels right down. I left hospital with a novarapid/lantus regime and was told to 'eat what I normally eat' so that they could gauge how MY body was responding to carbs and the insulin.
I did some research and of course found that my 'normal' eating contained too many carbs (not so much the obvious sugary rubbish like sweets etc, although I did eat some) but my 'normal' foods of wholemeal toast/pasta and a few too many ready made processed foods.
I am slim, very active, run a lot, don't smoke or drink so they couldn't really bang on too much about 'lifestyle' although they tried to. Anyway, I immediately cut out ALL processed food, and ALL the rubbish, obviously sugary stuff which are high carbs naturally and not healthy for anyone.
I continued with my toast/porridge for breakfast and my other normal foods, and the rest of the time, measured out very small portions of pasta now and again. I did this for the first few months and then after around 3 months (when I was more knowlegable and confident) I did away with the foods I KNEW raised my levels, ie, the porridge etc. Now I know you don't have to and type 1s can balance it with insulin but that is a personal choice. I don't think you should go cold turkey as it were right now because you do not know how your actions will affect the regime you are currently on and you don't want to risk having a hypo/hyper. Take it slowly.
My point being, please do not rush to immediately go 'low carb', it takes time for your glucose levels to settle/for your insulin doses to become correct and for YOU to come to terms with what's going on. Your low fat cheese sandwich will higher your levels, not the cheese but the bread. Please research foods because I (who thought I was a know it all about healthy foods) was almost ignorant on foods that massively raise levels. Hope this helps.