Hi @au0rei, yes the mesh was part of the surgery. They didn't decide to go over the muscle until after the mastectomy part of the surgery was done, then they could see I still had some good padding under the skin.
To support the implant, they create a sling for it using titanium mesh (safe for MRIs, Xray, etc). This is stitched on to the surface of the chest muscles to hold it in place.
You can't feel it, but it can be seen on an ultrasound. As I mentioned previously, there's quite a bit of stitching on the armpit side, as that's where gravity wants to take the impact, so it needs lots of support.
Best of luck with your upcoming surgery. I have posted my story in the Choosing Reconstruction group on here, it is titled "Immediate Over the Muscle implant Reconstruction" (or similar) if you want to look to have an idea of what to expect from the surgery.