Be careful about following recommendations. What is adequate for specific conditions varies greatly from person to person. Test it. Also be careful about recommendations concerning wetsuit thicknesses for specific conditions. There is a huge difference in the protection provided by specific neoprene thickness depending on the quality/expense of specific wetsuits - more expensive usually means better seam seals which helps determine rate of leakage and water flow through a wet suit. Good fit makes a tremendous difference. A loose wetsuit will provide nowhere near the water flow reduction that a snug fit does. Wetsuit seams wear out over time. Don't assume you still have the same amount of in-water protection from the cold as when your wetsuit was new. Test it.
There are hundreds of warm weather changing ponchos & towels. Below is a list of warm robes and changing coats for the cold. The southern part of the UK seems to be the world center of warm changing robes, but of course some of these companies have global manufacturing and outlets.
Patagonia: Quality is an environmental issue