Ive watched at the mountain mile before but it gets a bit chilly as the day goes on. I'd suggest bringing a flask of hot tea , a heavy coat and perhaps a winter hat. My wife (who's just had an operation) tends to feel the cold up there in the last few years so we've tended to park at the gooseneck and watch from there. It's a really great spot on the first lap.  Lots of people around, a lot of good old banter and is easily accessible for the disabled. If your hips are as bad as mine are you'll not have all that walking across fields. The toilets are clean too which is nice. And you have the added excitement of seeing the the teams signallers making up the pitboards for the riders. And there's refreshments there too. So you won't need that flask , after all!! All in all one of THE perfect TT spots. Let us know how you get on Sinty.