服 began with hands pressing someone into submission beside a boat-shape — to make obey, to fit to purpose. What fits the body became clothing; who fits your argument becomes convinced.
服 wears three meanings daily: 衣服 (clothes), 服务 (service — hence 服务员, waiter), and 服 alone for being won over: 我服了 ('OK, you win / I'm impressed' — the internet's favorite white flag, often typed as 服了 or just 服). 舒服 is comfortable — the body served well. From wardrobes to waiters to conceding an argument, 服 is about fitting.
Fitted to the body, fitted to the task — CLOTHES, SERVICE, CONVINCED.
我服了 'I submit' is modern slang for 'you got me / unbelievable' — surrender as a compliment.