People tend to assume that if you are in the tropics the weather is hot. At sea level this is true but not so at higher altitudes. This is true throughout the year. Rather than having four seasons, think two: wet and dry. And the temperatures are not really different in the wet and dry seasons.
A good rule of thumb is that the maximum variation in temperature between the hottest month (generally April) and the coldest month (generally December) is 5C. So, you can pretty much pick the temperature you like and then select an area at an altitude that offers that temperature.
The web site https://weather.com/weather/monthly offers decent information. Try Guatemala City, Guatemala for what is typical for much of the populated areas and Quetzaltenango, Guatemala for the cooler areas. You will see, for example, that 24/7/365 it will be 30C maximum and 10C minimum. In Quetzaltenango (called Xela locally but weather.com doesn’t know that) it will be a few degrees cooler but never down to freezing.
If you want to see an example of sea level temperatures, try San José, Escuintla, Guatemala for temperatures at the Pacific Ocean. There you will find highs in the mid-30s and lows in the high teens. Again, 24/7/365.