If the bolt is what broke, it can be replaced with a stronger one. Source would be a hardware store.
Otherwise the weak point in the suspension is the front swing frame. When you get your suspension out, you can see if it has any cracks/breaks. I believe if you get a newer one, they were built stronger, or you can reinforce yours.
You could put in stronger springs, but there should be no need to. I am a little above your weight and don't need to set the stock springs (which have a lot of years and miles of use) above the third setting for normal trail riding. Any more tension will make for a rough ride and put more stress (and more breakage) on the suspension components.
A good thing to do for reliability is to make sure all the nuts and bolts in the suspension are kept to the proper tightness. I have had suspension problems because of not making sure of that. While it is not something that has to be done, it is best to use a torque wrench on all fasteners. The service manual has torque specs.
