Numbers are way over 1,000 per day after the latest update from NATO. You can start with this one Russian Perspective

https://www.cnbc.com/2022/03/23/up-to-40000-russian-soldiers-killed-wounded-captured-or-mia-nato-says.html

This was my source for the 5k to 6k number. https://theweek.com/russo-ukrainian-war/1011133/more-russian-troops-were-killed-in-ukraine-in-2-weeks-than-us-troops-in