Try the custom AI to help you find products that Reddit loves.
I use the D'Addrio dual lock. What took me to those was the ability to loop the cord back into it to avoid ripping the plug out of the bass at an awkward angle in case anyone (me) steps on it. The third image in the link above shows you what I mean.
$3.99 worth of confidence
You can avoid messing around with your guitar by using "rubber washer" strap locks. They're pretty decent. Buy a reputable brand (Fender, Dunlop, etc...).
An even better option that the washers are these little guys:
Listed from cheap to expensive, but I use all of these everytime I play.
D'Addario Strap Lock with cable hook, this keeps you from tucking the cable between the strap and bass body, while also acting as an easy to remove strap lock.
Neutrik silent jack cable, it mutes the cable when you unplug it by using a tiny magnetic vacuum sealed reed switch. A guitarist tripped and broke mine so I bought 2 more, so I'd never have to go without it again.
Mono strap, I keep this on my heavy basses, it's extra wide and the padding is awesome.
Keeley Bassist compressor, if you really want to get him a pedal this one is great all around for tightening up your sound.
I do not have a bass with the orientation as yours, but I have had good luck with the D'Addario Dual-Lock Strap Lock for keeping my cord from wandering: