Bit of a misleading question then, asking us "does such a thing as a decent, lightweight sub-woofer actually exist?". I took "decent" to mean "capable" (not an unreasonable assumption), but it turns out you don't actually need 'capable'. Silly me, eh?
I'm impressed that you posted yesterday, then managed to do "a lot of research" and also buy a sub, all in the space of 24 hours. Why bother asking on here in that case?
Had you told us you already had a MarkAudio sub', we'd have likely suggested sticking with that (I would). 23kg is hardly a behemoth. I'm 72 and have no trouble schlepping my Fohhn XS22, at 25kg.