Q about insulin, beta cell rest

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11
Hello to everyone. First time writer, long time reader ;)

I have a question regarding insulin.. and resting beta cells etc. for anyone who may be able to help

As someone who controls my BG most of the time with Diet/Exercise i'm using Metformin at the moment to help me get back in line a little, but am considering insulin for those occasions i can't exercise or want a treat etc! I've used Sulfonylureas but can't stand them.

If my pancreas is only working at say about 70% (for example), if i take insulin to cover the other 30%, wouldn't i still be maxing out my own insulin, so is this resting my pancreas? If i was to take more insulin than i produce just to rest the pancreas (conserve beta cells), what tells my body to stop producing it's own therefore stop going hypoglycemic?
So i guess i'm trying to say is how much of the body's own insulin is used/needed when taken with smaller or even larger amounts of insulin? Will it be used in the background?

Thanks to all, cj