7 rows from the stage sounds very good, although being very short myself, I can understand the concern. Surely people in front and to the side of you will be standing, jumping, screaming, etc.
Even if the stage is elevated and you can see Michael from that vantage point, the mayhem around you might be very distracting if you really want to "watch" Michael and not be part of the chaos.
I've not been to the O2, but judging from many different views available to look at in this forum, the lower tier near the stage would seem to be better from the your height standpoint, and I would presume the jumping and screaming would still be there, but proportionately lower than your seat. The lower tier would have people in front of you if you're not in the first row, but would be lower than you are so that even them jumping and waving arms, etc., would still leave you higher than they are for visibility.
JMO, but enjoy whichever option you choose.