I had a single mastectomy nearly 2 years ago at age 52 and chose not to have implant/DIEP.
The scar is very neat and has faded almost away during this time. It's never bothered me. I'm not overly large breasted (10D), and it's very easy to just put a prosthesis in a regular full cup bra and no one would ever know - I have a few different prostheses, and they fit into all my non- mastectomy bras :)
I couldn't parade around openly with the scar tho, that's just me.
I made the decision to stay flat in order to avoid further surgery/scars/possible complications. And I didn't want anything (infection etc) to delay my starting chemotherapy.
It really hasn't been a big deal, and I don't feel any less attractive for it. And I was happy for the cancer to be out.
PS - the option is always there to have an implant or DIEP at a later date.
All the very best with your decision and journey.