Also bear in mind that humidity may play more of a role than temperature, and I think you're in a region where that can get very humid too. In general I'd expect that temperature affects mostly if not only tuning (as long as we're not talking about freezing or cooking temperatures
I was surprised to learn that nylon strings are apparently sensitive to humidity, and out of experience with (plain) gut violin strings I know that this can really change the sound quality (as well as intonation). Using oiled gut strings was the solution for me (lasted longer, too).
You could try to treat your regular strings yourself. There are "fast fret" applicators which protect metal strings from corrosion through a very thin oily layer. That should help against moisture too. Better yet: try treating your strings with linseed oil (during dry conditions so as not to trap moisture inside; no need for high-grade food quality oil unless you want to make healthy salads too). Just put some on a kitchen paper towel and wipe the strings with that to put on a thin layer without any excess. Linseed oil has the property of drying when exposed to air (hence its use in paints) but should remain flexible. Note that I have no idea what it does to sound; I do know however that the "fast fret" stuff I use doesn't change the sound but *can* help to reduce buzz.
Mimmo from Aquila strings is on this forum; try shooting him a PM if he doesn't find this thread. He should be able to give advice if there's any kind of conditioning you could try, and he certainly should know if they have lower tension nylguts.
Gretsch G9240 "Alligator" wood-body resonator converted to non-metal strings (China, 2018?)
Bolink baroque violin (Hilversum, 1982)
Formerly: Brian Cohen baroque violin (London, 1985), Nadegini modern violin (Paris, 1924)