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Clothing for shoulder monthes between Winter and Summer, or mixed conditions - not cold water, but maybe cool water and medium to warm air temperature, etc. - you have to figure out what your in-between conditions are and what provides adequate protection.
Before you rely too heavily on these styles for warmth you should test them in the conditions you intend to use them in. Farmer Johns/Janes can be deceptive - providing a fair amount of warmth while you are dry, but providing surprisingly little protection when wet or submerged particularly if they are the style with long zippers - often such zippers and/or the suits simply allow too much rapid water entry and exit to slow heat loss. If paired with a snug top, water flow-thru rate can be reduced.
Many other wetsuit brands offer farmer johns, janes, and shorties