This is such a complicated issue. Some people just have genes that make them more insulin resistant, but there are things that can increase, like being overweight, or other things.
But the thing is if you are prone to being insulin resistant it will mean that your insulin producing beta cells will have to have worked very hard, and might have got a bit tired, and be producing less. Which might well be the reason why you are now having to take insulin.
On the issue of your blood sugar going up over night this can often happen to people with Type 1 diabetes, when there is something called dawn phenomenon where the adrenal glands start working in the early morning, and the liver pushes out glucose, and blood sugar starts to rise. So that might explain the overnight rise.
Also your breakfast carb spike took you back down to 4.2 which suggests that the insulin is working reasonably well in the day time, because your breakfast was quite high carb, porridge spikes blood sugar quite a lot, and bananas.
I think that shows the insulin is working, and if you feel better using it, than the previous medicines that seems like a good thing.
I found this article on insulin resistance, below, that seems quite good. You may want to reduce your carb intake a bit, at least for a little while, because managing carbs and insulin is complicated enough with Type 1 diabetes, throwing in a bit of insulin resistance makes it even more complicated.
But getting down to 4.2 suggests it is working, so keep an eye out for hypos.
http://www.diabetesforecast.org/2011/jun/understanding-insulin-resistance.html