I'd go with a good-quality 20W USB-C charger from Apple or a reputable brand like Anker or UGREEN. The iPhone will only draw the power it needs, so using a 20W adapter doesn't mean it's always charging at full speed. If you prefer slower charging, a 10–15W charger is also perfectly fine, especially for overnight charging, and may keep temperatures a bit lower. The important thing is using a reliable, certified charger rather than focusing only on the wattage.