I had a double at 43. I knew I would never be able to trust the second tit. Had tissue expanders reconstruction done at the same time --which if I'd known then what I know now I would not have done. But that's a different story and more about the way I scar than anything else.
If you are big breasted and go for a single, the current advice seems to be that you should plan to wear a prosthetic or consider reconstruction, not for cosmetic reasons but to try to avoid back and shoulder pain associated with being unbalanced physically. Talk to the breast care folk.
Personally I didn't find the decision to get rid of both any more challenging than the realisation that one had to go. Back in those days the surgeons up here wouldn't do it ( still reluctant from what I heard yesterday) so I ended up in Melbourne at Peter Mac. That certainly influenced the reconstruction process which I may not have bothered with if I could have had a double performed locally.
I've had a recurrence after ten years anyway, but at the time I felt I had done everything I could to increase my chances of survival.