A couple of things have made buying embarrassing or unusual items easy for me.
When my daughter was born in 1965, my wife remained in the hospital for nearly a week after a difficult birth. My wife and a nurse instructed me to go out and buy a certain type of bra for my wife. They were very specific as to the size and style, but didn't specify a certain brand. So, being the proud new papa, I went to several stores and spent quite a bit of time checking bras and finding the specified bra ( Even back then, "Customer Service" left a lot to be desired). It was embarrasing as heck, but I did it. When I got back to the hospital with my prize, I thought my mission was done. My wife tried on the bra with the nurses assistance. It was perfect, so the nurse said "that's exactly what we needed, now go back and get two more"!!
After my wife got home, she was still bleeding quite heavily and was pretty much restricted to the house for an additional week or so. So, it was left up to me to go to a drug store and buy a big supply of the large heavy duty "Hospital Style" pads. I ended up with a shopping cart full of pads, much to my embarrassment.
From that point on though, I have no problems buying embarrassing things. I find what I want and head for the checkout. Nobody has ever made any comments ( I suppose they might have wondered what I was up to). I do live in a smaller town, and do try to avoid bumping into a neighbor or aquaintance, but othet than that, no problem!!
Just go into the store like you know what you are doing, get your stuff, pay for it and leave. It's that simple.