“Modern block sizes” will vary where you live, and you can build smaller of course.

Obviously this is location dependent advice. If you live in a lifeless suburban wasteland, then outside is no better than inside. If, on the other hand, there is nature around you, and it doesn’t get too cold in winter, then insulation is a pointless exercise! Get a ceiling fan and learn to tolerate a bit of heat.

I, personally, need nature to stay mentally healthy, and having nature wander inside from time to time helps greatly.