I added the baking soda brcause when I was looking up info on soaking it was recommended to use the two together plus add essential oils for various reasons. I got the epsom salt that already had lavendar in it so I used that plus the baking soda. As an example this site even says the baking soda will help absorb the magnesium in the epsom salt...
http://www.branchbasics.com/learn/espom-salt-bath/
I didn't have any skin sensitivity, just joint pain a bit worse than I'm used to waking up with, when I sort of expected it to be better. Thank you for your help Mrs.D