It's quite some time since I read either book, so apologies if my memory fails me here. Terry Nation's book of the tv series Survivors (which ends quite differently to the television programme) may be worth consideration.
Incidentally, the 1981 tv series 'Day of the Triffids' is well worth a watch if you haven't already seen it. Much better than the movie or the more recent tv drama.
I saw the 1981 tv series on PBS. Yes , it was very good indeed .