Chumphon Airport (CJM) does not operate a dedicated passenger lounge, and the honest reason has as much to do with what the airport is for as with its size. Chumphon serves as the closest airport gateway to the ferry piers for Koh Tao and the Chumphon archipelago's diving crowd, so most travellers here are moving quickly between a short domestic flight and a ferry connection rather than settling in for a long wait.
That connection shapes the airport's rhythm more than anything else. Traffic through Chumphon swells around the high diving season, roughly December through March, when ferries to Koh Tao run heavier schedules and flights fill with divers and backpackers timing their arrival to a boat departure. During the wetter months later in the year, ferry frequency and flight loads both thin out, and the terminal returns to a quieter, more provincial pace. Neither season has produced a lounge, because the through-traffic model rewards a fast walk from tarmac to ferry pier rather than a long airside wait worth building a lounge around.
For travellers who do want lounge access on this kind of trip, the realistic move is to build it into the Bangkok end of the journey instead. Suvarnabhumi Airport (BKK) and Don Mueang Airport (DMK), the two Bangkok gateways most Chumphon flights connect through, carry genuine lounge networks, including Priority Pass style options and airline clubs, in a way a small regional field built around a ferry pier never will. If your itinerary allows a longer connection in Bangkok, that is where a lounge visit belongs.
Chumphon itself is worth planning around its actual pattern: light domestic terminal facilities, a short walk to onward ferry transport, and traffic that follows the diving season rather than a business-travel calendar. Treat any lounge ambitions as a Bangkok-side plan and Chumphon as the fast link in the middle of the trip, and the itinerary works with the airport rather than against it.