I also have Dcis, though I have been offered a mastectomy due to previous surgical margins not being clear. I assume this is why you have been offered therapeutic mammoplasty? Has the surgeon also offered surgery to your other breast to ensure you end up with similar cup sizes? I understand this procedure is offered to ladies with a larger bust, and that it is not a procedure done in all nhs trusts. Hopefully there will be another forum user who has already had this type of surgery and can offer some support. If you are struggling with deciding whether or not to go ahead it might be worth speaking to your breast care nurse, they can go through any options again with you at a more relaxed pace.
Welcome to the BCC Forum. While you are waiting for other members to respond, I thought our factsheet on DCIS might be useful. I've attached a link:
Very best wishes