Too hot for baby

I just had my son on Friday the 20th and since it’s been crazy warm out around here, well crazy warm for April. It’s been anywhere from 18-20C (64.4-68F) but my apartment is also a top floor unit on the west side so sunlight gets directly into our unit all day long and it gets around 25C in our home (77F) So sometimes my baby boy overheats. I’m so worried for William because I know it can be really bad if an infant, especially only a week old, overheats too much and it’s only getting warmer here. I need tips and safe ways for keeping infants cool. We might move to a different unit out of the direct sunlight later in the year but right now we just need ways to keep William cool.