In some aircraft the life jackets are no longer under the seats but are stowed in the overhead with the lights, air con blowers and O2 masks. Worth listening to the briefing and finding out which applies on your flights don't you think? Speakimg as someone who has been SLF for over 50 years and always listens to the briefing - no reason not to!
There are also different models of life jacket, some have clips/straps to secure them and have long tapes to tie at the side. Again, worth knowing before the water laps round your ankles!