For others who might stumbled on this, we've always managed to find these laundry place on the Kowloon side, found them near Langham Place, in Mong Kok MTR - where locals lived & worked, that charged by the weight (a typical laundry bag full - 10 to 12 kg. done, dried & folded by end of day by $50 to $60 HKD (dirt cheap, including socks & underwear) whereas hotel would be charging them by the pieces.
And, there's always paper underwear ... disposable & all (no, we don't use them, but know of others.