Hi, Karen. I think you made a wise decision to wait for the surgery until you could research and decide what is best for you.
I had a TRAM -flap many years ago. Results vary with the surgeon. One of the best looking TRAM-flaps I've seen was on Desertdreaming. She had a bilateral a couple of years after her double mastectomy. She has absolutely great results! Very natural looking.
Because you are having a bilateral, you won't have to worry about weight gain or loss. Whatever happens to one side will happen to the other...those of us with just one side reconstructed are the ones who have to worry about that. I'm surprised your SIL didn't tell you that.
As far as I know, anywhere they take tissue for a reconstruction is going to involve losing muscle somewhere. I'm not that "up" on the microvascular surgeries, so forgive me if I'm totally wrong about that. I know when I had the reconstruction, it was the belly, the back, or the butt. The belly was the most popular because it gave a bonus "tummy tuck."
Since you're having bilaterals, I would think about plain old implants. You wouldn't have to worry about losing muscle anywhere, the procedure is much less invasive, and any good plastic surgeon should be able to give you a good result.
And Erin, we did have another friend whom we have since lost who had a bilateral Lat Dorsi with implants. She, too, had a really nice result.
Good luck in your decision, Kathy. And good for you for making sure you had time to look at all the options!