too many foods contain too much salt
I'm glad to hear that you've discovered the dangers of salt. It is quite literally a killer. You should try not to take more than 6g per day. You should watch your children's diet too. Research shows that even young children who have a salty diet, have elevated blood pressure for their ages. You'll struggle a bit Paw, because you like many of the traditional Polish dishes which are heavy on the salt and fat. However, it's worth it. It does mean though that you'll pretty much have to cut out the wędliny, sausages, and even the smoked fish in large quantities. At least you prepare quite a lot of your own which means you can control the amount of added salt.
Butter is actually not too bad as Jon says. The amount of salt added to Kerrygold for example is 1.8g per 100g but you don't use that much butter on bread or even on spuds or whatever. If you use it once a day on your toast you'd be ok and good quality butter like the Irish stuff has lots of nutrients and vitamins which are beneficial unlike things like ketchup which are loaded with salt but have no benefits at all.
You can counteract the effects of salt with certain foods. Beetroot is great because it's loaded with potassium which lowers the blood pressure. Fresh beetroot juice every day, or fermented beetroot juice are both ideal. Of course the stuff in the shops has added salt! So make your own. Also extract of olive capsules, 1000mg per day has been shown to lower blood pressure by up to 10 points. You can use it alongside regular blood pressure meds and it helps to keep the dosage of the meds lower. They use it in hospitals in Australia for treatment of blood pressure patients as it's so effective.