Going for a swim in the our ocean in the summer, which i love to do to in my bathing suit, cant be compared to diving. You are going to want a proper wetsuit with gloves, hood and booties, or a drysuit. I wouldn't dive locally without a drysuit, the dive duration would be way too short for me in a wetsuit. You can wear wetsuit boots over the soft sock drysuits instead of a lace up drysuit boot as long as the wetsuit boot is big enough. Some drysuits have an attached boot which is rigid. Locally you will be in a 7mm boot for exposure protection. The ocean is 7c right now.
Wise words. If the OP plans on diving locally, dry would definitely be the way to go.
There is a HUGE difference between splashing around in your board shorts for a "little dip" and spending 30+ minutes underwater where the water is 7C at the surface, but drops at least a couple of degrees when you are at depth.
FWIW,