Trying the same thing now. Booked commercial ticket. When trying for direct upgrade it is not available. So I booked a business award on waitlist. If wait list clears I intend to user it for the economy to business upgrade
Are you able to waitlist the upgrade?
iirc, the booking class for full redemption and upgrade is different. So say your biz class full redemption seat is confirmed, you can't use it for upgrade from a paid economy ticket to an upgrade biz class seat. Cos there's a different quota for different seats. Likewise, if your upgrade seat is confirmed, it can't be used for a full redemption.
There have been conflicting information about this. Though they book into the same fare class technically, people have reported that although there might be saver award available yet the upgrade does not go through. However, calling might help with getting the upgrade to take the available inventory.

