As mentioned in the Small Forward piece, the Thunder do not have much frontcourt depth heading into next season. The starting three and four looks to be Darius Bazley and Kelly Oubre Jr.
It is also entirely possible that Kelly Oubre Jr is traded before the December 22 start. On the bench, the only forward who is contracted for next season is Isaiah Roby. Mike Muscala has a player option for 2020-21 that he is likely to opt into.
In a similar vein to the other positions, a free agency acquisition will be relatively cheap.