Needing a mastectomy but not sure about reconstruction...!

I have been diagnosed with high grade DCIS and have had two excisions but not clear margins. I am having a mastectomy and I cannot decide whether to have a double or single with implants or a DIEP single (not enough tummy fat for two!!). I have been reading a lot and speaking to lots of lovely ladies but I am more confused than ever. I am worried about the implant going UNDER the pectoral muscle. Who has implants under the muscle and how have you found its been? I would really welcome some honest comments. C