Hi Sarah,
I had a breast reduction back in February. It was a huge decision for me, but I have not regretted it once. The surgeon had warned me that I was at greater risk of complications, wider scars and longer healing because of my diabetes. I have had no issues whatsoever. My checked my hba1c at my pre op and said that I would have been ruled out if it was considered to be too high; it came back at 5.something so I was fine. The only thing I would suggest is that you keep control over your own insulin when you're in hospital. I was put on a sliding scale ahead of the operation and they kept me on that for three days as u was quite immobile. If I was to do it again I would have definitely ask to be taken off the sliding scale once I was recovered from the general.
Finally, check out a site called breast health online. There are loads of people on there who have had breast reductions or augmentations. Like this site it's great for general advice.
Hope this helps. Feel free to ask any questions. I know I had loads ahead of my surgery!!
Em xx