I've been looking around this forum and some others as well, and I hope I find some knowledgeable advice here. I just purchased a home w/o AC and with floor furnace. so we want to update all of it because it can get super hot and mildly chilly. The house is about 1200sq, single story, old (60 yo). How big of a/c and heating unit should I look for? Any brands I should be aware of? Any other advice is very welcomed!

Thanks in advance!