I took a fairly long time over it, about an hour. I made the status of the top right corner to be
that White has to play a two-step ko in order to kill Black.
I considered immediately fixing the aji in the top right but that seemed unreasonable as White had already concentrated his forces so much there. I also had some ideas of
living in the lower right corner (didn’t seem possible), sacrificing the stone there (perhaps sometime but not immediately), and making a cut to introduce aji for later (seemed reasonable.)
The first move I instinctively wanted to play was
G4, strengthening the K4 stones whilst weakening Black’s stone. However, I didn’t like the variation from Black’s response H5 which saw White sealed into the side.
The final move I examined was
the one I was happiest with: the same idea but a line higher, at G5. It appeared to be harder to push White down, and if Black took the base at H3 then White had a series of forcing moves to gain robust shape and even finish in sente.