OSX Yosemite suggesting updates, I don't want to upgrade, but need to upgrade iTunes
Always check out Apple Support

https://support.apple.com/kb/dl1977?locale=en_US

There is a link to a 10.10.5 compatible version of iTunes 12.8.2. You must click this link for the 10.10.5 compatible version.

https://secure-appldnld.apple.com/itunes12/041-37721-20190206-950874F8-AAA0-4373-96E9-A995A9B354C7/iTunes12.8.1.dmg

The 'Read before you install iTunes' document that is within the DMG states that 10.10.5 is supported on this version of iTunes.