Well, it depends on you technique. I personally do not need a bout for the left hand that much, but I think classical players (who play the bass bowed almost all the time) need a left hand shoulder to be able to hold it properly.
In my opinion a shoulder on the other side, which will lean to your body is almost necessary. The bass will turn around otherwise. I once played a bass without any shoulders, which was terrible to play.
Unless....you place the bass on a stand. I do not like it, but it is stable for sure! :)
Sndr
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