Lazar Kaganovich
For those unaware Lazar was very much a yes man of Stalin, why am I choosing him? Mainly because I feel choosing someone very firmly entrenched in conservative circles could argue reforms are needed would be listened to and if guilty enough they would trust him he would not seek to demolish a system that protect him.
While it's definitely likely reforms would be watered down I feel a radical reformer who needs to placate conservative voices would face similar situation.
Though, on the topic of the Baltics, I'm willing to accommodate Latvia and Estonia but not entirely sure about Lithuania, by that it's quite imporant for keeping control of Poland plus Kaliningrad. In fact If we could I'm very tempted to merge Kaliningrad with Lithuania to improve the viability of it and secure the Baltics more or play around with their borders.
After the Baltics without coastline are no real threat and so can be accommodated a lot more, plus one of the USSR's mistakes was largely preserving the old Baltic nations borders.