I've been hunting down old kung fu flicks on lazy Sunday afternoons, so when you say 'the movie featuring
the big boss' my brain immediately jumps to the classic Bruce Lee film 'The Big Boss' (1971). If that's what you mean, start by checking the usual digital storefronts: Amazon Prime Video, Apple TV, Google Play Movies, YouTube Movies and Vudu often have it available to rent or buy. Availability swings by country, though—I've rented it on Prime in one region and seen it pop up on a free, ad-supported service in another.
If you want to avoid rummaging through each store, use a stream-finder like JustWatch or Reelgood, type 'The Big Boss' (or 'The Big Boss 1971' to be safe), and set your country. Those services are lifesavers when regional rights are a mess. Also don’t forget library apps like Kanopy or Hoopla—my public library surprisingly had a few martial-arts titles I wouldn’t have expected. For a no-frills route, classic-movie channels and specialty services that focus on Asian cinema sometimes run it seasonally, and physical copies (Blu-ray/DVD) are great if you want the best transfer and extras.
If by “big boss” you meant a different film or a character nicknamed Big Boss, tell me the actor or a line of dialogue and I’ll narrow it down. I love these little detective hunts—finding the right release with decent subtitles feels like winning a tiny treasure chest.