Best way to strengthen a wheel?
When the spokes break, do they snap at the J bend?  Or elsewhere?

If the little mushroomed cap is gone at the hub end and there's a spikey "claw" then your spoke tension is low which is stressing then tensionining the spokes on every wheel revolution.  

I'd start by lightly tapping the wheel spokes with a screwdriver, key, or something light.  And then compare that TINK sound with other bike wheels.
Or if you're a hands-on person then gently squeeze two spokes somewhere outboard of where they cross.  Compare that hand-feel with other people's bikes of similar wheel size and construction.

I think you could probably tighten every spoke nipple by a half turn or even a full turn all round.  Be aware that a weak spoke might choose this time to let-go.  



If you don't feel up to all the messing around, there's no shame in taking the wheel to a LBS for a professional build.  A good wheel is the ultimate outcome here.

Do you know what pattern its laced with?  Radial spoking is rarely if ever done on the back wheel, so you're likely to have some cross pattern.   2-cross or 3-cross are most likely.  If you have a 1-cross then the spokes don't leave the hub at a great angle, and are not far off radial, so this stresses the spoke's J bend more than 2/3/4 cross.

No idea how large the nuvinci hub is, but I've put an alfine11 in a 26" wheel and had to go 2 cross.   I guess you'd be best with 3-cross on a 700c (29") wheel.

Thicker spokes is always an option too, but if you do this then the whole wheel needs relacing.  I wouldn't mix gauges on the same side, though I might accept having a different gauge on the left vs the right.

I'd probably go with straight spokes.  The cost of butted, double and triple aren't worth it, they're more for weight saving than adding strength.  Butted spokes have a thinner piece in the middle which can stretch a little more under impact, leading to a "better" ride.



Aside, 95 kilograms is not ridiculously heavy - I was there only 6 months ago.
 Sure we're more than a GCN rider in their 60s and 70s, but more mass means more muscle, right ?

You might not be good on a svelt road bike but I'm guessing you're on a rigid commuter/hybrid bike.   Your weight is not the root problem here, though it will make potholes much harder on your bike, and brakes will wear a little faster.  On the upside, more weight means more exercise per metre travelled.

The hub is probably not really helping, given its a lot of weight compared to a 100 gram hub and a 400 gram cassette etc.  The hub's position means it has the least "suspension" effect and can make the wheel harsher.  If your bike has rear suspension, the hub is still unsuspended weight and that contributes to the impacts, stressing those spokes.

Basically don't ride off kerbs/curbs and don't bulldoze your way through potholes or speedbumps.  Learn to unweight your saddle, then "ballerina" your bike as it passes over the obstacle, effectively halving the weight for an instant.  You're not trying to get air or off the ground, just unweight for a brief instant.  Timing is everything and cleats can help a lot.



The eyeletted rim is only relevant if you're causing damage to the rim.  If the nipples are pulling through the rim holes then you would benefit from eyelets.  I doubt this is required in your case.

A bigger tyre would be great if you can fit it in the frame.  I rode 23mm for a while, then went 28mm and then 32 for a short while  Each step was an improvement in comfort, but other changes meant I had to return to a 25mm on the current road bike. 

The pinch points are your chainstays, seat stays, and rim brake bridge or calipers if you have them.  Sometimes mudguards can be limiting too, but they're easier to adjust than the frame.