Guitars are made of wood. Wood absorbs moisture. New strings have different tension. The guitar will settle down after a little while. You should get used to adjusting the truss rods so that you will be in control, not the weather. My luthie said a long time ago, all guitars are happiest in their cases, not out in the room or out at a gig. If you can control the humidity in your home with air conditioning, leave the guitar in the case in the AC controlled room. You will see a better behaved guitar. For a fretted bass you can try any non-coated round wound string as long as your fingers can handle it. I like Long necks DR strings for my fretted 6 string Europa. These are stainless steel strings. They are very brite, and strong in the low end, and last a long time. Not sure if you can get them in your country. Rotosound is the original stst round wound string, but they eat frets and don't last as long as DR's. Try Alembic's string. It is a pressure-wound round wound and sounds great, and gentle on frets and fingers.
