@NorthLondonRef
Law 12: "Where a player commits an offence against an opponent within their own penalty area which denies an opponent an obvious goal-scoring opportunity and the referee awards a penalty kick,
the offender is cautioned if the offence was an attempt to play the ball;"
I can see that in your posts you have agreed the goal keeper has attempted to play the ball (albeit a risky one). That would be sufficient ground for not sending him off.
Also form your posts I feel that you take the guilty until proven innocent approach.
There are numerous FIFA and FA educational videos on the 'new' DOGSO yellow, with many similar to this incident instructing to issue a yellow card only.
Although this is one of those which is ITOOTR and you are entitled to yours as the referee, for consistency sake I would recommend to opt for yellow if this happens in your games.