I was more interested in your question:
"an inflatable rubber saucer is you only and/or best solution in case you
are
sinking?"

What other options are you thinking about?

1.) A hard dinghy, ala Lin & Larry,
2.) Putting the boat in solid shape,
3.) Realizing the chance of a sinking is remote compared to other risks,
4.) Realizing that maybe -- just maybe -- an inflatable rubber saucer might
not inflate when you need it, so plan to not need it.