All you need is a simple analogue watch, preferably with a rotating bezel marked in minutes.
Many years ago I thought I needed a stopwatch so bought a Citizen diver's watch. It's an excellent watch, but although I use the rotating bezel every time I fly (to mark a time) I hardly ever use the stopwatch.
If you decide to buy a chronometer (not needed) make sure it has a sweep minute hand (one rotation for a minute) and a readable dial for elapsed minutes, mine has 60 minutes on a tiny dial and it can't be read accurately in flight - some have 30 or 20 minutes on the dial so are much easier to read.
HFD