Don't spend beyond your means during your working life, dont have too many kids, 2 is enough to replace you and your partners DNA when you die!
In todays money, if I was mortgage free, I could easily live on a retired income of about £1000 a month between me and the mrs. A combined pension (be it an annuity, savings interest or whatever) of less than £12K a year is not that hard to amass imo. Hell even one good fully paid off investment property + basic state pension would hit that mark without much trouble.
No mortgage, no kids to support, just quietly enjoying life somewhere tranquil and idyllic. The Simple life.