I’ve liked my thermal tights from 2XU. Had them since 2014, and used in negative Cs (maybe down to -5C?). Feels very chilly when you first go out, but then gets quite comfortable once you get running.
I can’t run outside myself until Spring now myself - suffering from runner’s knee now and slowly recovering, but it can still start hurting in the middle of a run. Having to stop to walk back in the middle of a run is not ideal when it’s cold outside and you are dressed for running and not walking.
Why wait?