Originally Posted by
SFO_FT
(1) assign you a seat and put what's called a "soft" block on the seat next to you and/or (2) put a comment in your record indicating that you might need for the "airport control" desk to block the seat next to you.
Totally agree with all the above comments and well done the OP for posting on such a sensitive topic. However, I personally don't believe it is appropriate for the airline to offer either of the two options re blocked seat at no cost.
I think OP suggestion that he pay for a an extra seat is a much more reasonable suggestion and equitable to other passengers who presumably might also enjoy the space of a free seat next to them.