A goiter is an enlarged thyroid (the thyroid growing large itself). A mass or a nodule is more like a growth or tumor growing on the thyroid---sounds more like what you are describing. These are usually benign, but the right thing to do is to get it out, as yours is on the larger side for these things---as a normal thyroid lobe is about 3-4 cm in size, so yours is comparatively large for the area.
I found a 2.5 cm nodule, I felt fine, no thyroid issues, I had a needle biopsy. Did you have one yet? What were the results?
If they only take out one lobe, you might not need to be on medication. The medication is not really medication, but replacement hormone. I've been doing fine on it. I actually had thyroid cancer---you likely don't, but if you do, it's easily treatable, and usually curable, unlike others.
I thankfully live a full and busy life without my thyroid, I don't miss it at all. You need to have a good attitude to go through this crazy stuff.
Make sure you have a great surgeon that you feel confident in. Mine had a great deal of thyroid experience, and that made the process much easier. I had a weak voice for a couple of months, but then I was fine. I didn't have any calcium issues, but that is something to watch for after surgery.
As far as surgeries go, this one was pretty easy for me, I was up and about pretty quickly, and went to some family events within 2 days.
Good luck with your surgery, hope it's as easy breezy as mine was, and wishing you benign results!