The Pentax K1000 was in production for 21 years. 21 YEARS! What made it so popular? Simplicity? Durability? Ease of use? All of the above?
The Pentax K1000 is very likely the 35mm film SLR camera you're looking for.
In this video I talk about the K1000, what makes it special, and also talk a little about one of my favorite photographers who is famously Pentax user: Glen E. Friedman.