For context, I'm looking to do research for a story about a Russian character who was a soldier during World War 2 and later became a cosmonaut, so I'm mostly interested in the early years & cold war era. I've looked at the reading recs for Russia on this sub, but it seems like most of the suggestions are concerned with the later years.
For the Stalin period of the 1930s, many of the works by Sheila Fitzpatrick are valuable such as Tear off the Masks and Everyday Stalinism which provide a good introduction to life in this extraordinary time. Daily Life in the Soviet Union by Katherine Bliss Eaton covers a number of aspects of the lived experience. For the post-Stalin generation and youth culture, Juliane Fürst's Stalin's Last Generation covers the period rather well. The oral history Soviet Baby Boomers: An Oral History of Russia's Cold War Generation also gives a window into the daily lives. Slava Gerovitch's Voices of the Soviet Space Program Cosmonauts, Soldiers, and Engineers Who Took the USSR into Space is an oral history of the Soviet space program and worth a look given your plan for a cosmonaut character. The author for the Soviet space program Asif A Siddiqi who has written doorstopper books on the space program as well as edited a good anthology on the intersection of space and Soviet culture, Into the Cosmos: Space Exploration and Soviet Culture.