That's very nice for you, but your company should be aware that the IRS does not go on trust and so it will need receipts to substantiate those business expenses!

Anyway, if you fly BIS 120k a year, then I would start out with a status match to DL (if you're not already there; sorry I can't see your profile there), maybe buy some A tickets at first but once you reach DM (which you should be able to do BIS based on occasional premium fare purchases), most of the time you should buy the cheapest available coach fare or at least something fairly cheap like a K. That should net you >95% upgrades if you also invest in a tool like expertflyer or KVS to give you a sense of how wide open F is when you buy your ticket. Obviously on DM-heavy routes like long-hauls out of ATL or JFK to SFO/LAX you may not want to risk it and instead buy first outright. But most of the time on a T fare as a DM you'll snag the upgrade.