Without any pics or video I can only guess.
Bent left hand wrist strain often comes form left elbows tucked into the body.
Maybe raise your left elbow up and away from your body to minimize the left wrist bend
Many players get recommendations about how to position the bass
usually half informed for their specific situation - "same strap length sitting or standing" , "raise /lower the strap" etc
They try to follow the advice
bass first , and then contort their unique body geometry to this generically recommended bass position.
the real trick is to figure out how to position your body, arms and hands comfortably
and then reposition the
bass to suit what is comfortable
so sit, put the bass in "classical guitar" position on your left leg, put your right hand in pluck position, left in fretting position
and ask yourself:
- how can I move my bass to make this more comfortable?
- how can I move my body to make this more comfortable?
take a half hour to figure out the unique biomechanics
you need to have comfortable left and right hands.
OP also does not mention if they are 1FPF slave... 1FPF can be straining on a full scale instrument.