The book "How the Fender Bass Changed the World" has an interesting survey of all the ways people tried to have bass instruments that were less troublesome than the double-bass (and they could have included tuba and bass saxophone, which are also unwieldy in their own ways) before electronics. Mandobasses, bass balalaikas, the Bassoguitar, enormous banjos, it goes on and on. Finally we reach the conclusion: there's kinda no substitute for a double bass except an electric bass guitar, which makes up in convenience and loudness for what it gives up in authentic duplication of the double bass sound.