The IL-4 or Tu-2 would be the best Soviet bombers to add, imo. No doubt, the Soviets need a level bomber.
The IL-4 due to its service throughout the war. It had a good range of 1600 miles albeit only 2200lb of ord capability. However, the IL-4 could carry 3 torps! It was the Soviet's main bomber that attacked Berlin on a consistant basis. It is sort of the He111 of the Red air force.

It remained almost unchanged from 1937 to 1945. Over 5000 were produced.
The Tu-2 was a late war (June 1944) bomber that is able to hammer ground targets both via level bombing and direct attack by using its 6600lbs of ord or its dual wing mounted 20mm cannons. Its max speed is 340mph at 17,000ft. It has a range of 1200 miles and over 1100 of them were built.
The Pe-2 would be a decent addition for a light bomber I do suppose. It was able to carry 2600lbs of ord, but was weak in offensive guns. My data is showing it was used as a dive bomber and not a level bomber, but I'm sure someone else is able to comment better. Oh, it did serve throughout the war and over 11,000 of them were produced.