depends on many factors, one is certainly where the hernia is.
Anyway, the weight of the instrument is one element of a complex equation with at least 3 different variables. You, the horn's weight and the playing position.
Flute, the lightest instrument, would put some strain on the shoulders, there are flutes with a modified headjoint to allow it playing in a straight position.
It is even possible to put a recorder headhoint to a concert flute. These are either modified Alto recorder headjoint or specially made fipples.
The alto, obviously is the heaviest one but you can buy a Vibratosax which only weights about 1Kg. This is very light and if played with a harness or something to take the neck strain should't put too much pressure anywhere.
The least flexible here is the the clarinet and no so much because of the weight. You have Synthetic clarinets and also the NUVO clarinet which is completely made of plastic. But the playing position (even if you put a strap) necessarily imposes some postural problems .
I would go for a flute modified to play in a straight position ( even a Nuvo flute, made of plastics) or a Vibratosax with something like the Saxholder.
