You are correct to paint the surfaces. I recommend a product like this.

The humidifiers you have chosen are too small. Get two, one for each side of your home. And get bigger ones. Maybe like this one.

I would also take pictures of the water condensing on the walls. Document everything you are having to do including the money you are having to spend to make your home "livable" and protect the property of the the landlord. Stay in communication with the landlord and ask if you can deduct some or all of these expenses from the rent since you are helping to prevent mold damage to the property. Mold is dangerous and it is nothing to mess around with. I don't know what the laws are where you live, but the landlord should be inclined to help with this problem.

If the problem persists or the landlord is not responsive it might be a good idea to find another place to live when your lease is finished.