Have you been to look round the 2 Romsey schools and the (3) Winchester ones? I am a parent at one, and know parents of children at all of the other 4. There are aspirational kids at all of them.
Don't go on outside impressions or hearsay. Go and look at the schools.
My DD has come on in leaps and bounds at secondary. True, you have to work, but they do have systems in place to warn you of behavious issues and I have found it was easy for DD to get moved away from a disruptive pupil when needed.
DDs school certainly celebrates success and has aspirations for all its children. However, for some children, maybe success is less academic than for others. But they do have children coming out with 10+ A/A* which should be enough for anyone really.
Better to save your money for occasional tutors if you really feel the need. If your DS is only 8, he has loads of time to mature, especially with supportive parents behind him.
ps Watch out for Kings. It streams as well as sets, and the streams are very visible to everyone.