Hello, I have a larger intex pool and a different model. I live in Oregon so I think our weather is similar. I’ve done a lot of research on trying to heat the pool. I definitely second the recommendation for a solar cover (the ones that look like bubble wrap). I also use several 2x20 ft solar heaters. I’ll post below. With a pool this small you could probably get away with using one or 2. You would need a place to put them where they can get direct sunlight. I set mine on my roof during pool season. Other types of heating would be very expensive due to heat loss from lack of insulation.

https://www.amazon.com/SunHeater-Solar-Heater-10-Year-Warranty/dp/B09SQB9XRL