I've certainly done longer - north of Peterborough to Tower Bridge (and then a ten min walk). It's doable but exhausting. Worse in winter when you never see daylight and you feel chilly and damp all the time.
Currently (outside Covid) north of Bedford to London, about an hour and a half each way, 5x a week. Bit easier. Can't nod off on the Thameslink trains though, they are way too uncomfortable, rattly and bumpy. From my stations I do at least get a seat both ways, that helps. Standing all that time is miserable.
I do earn more though so for me the cost was worth it.
Three days would normally be season ticket, you get the saving on the third day for the train. There's also value in not having to book every week and get there early to pick up your weekly ticket and to having a scannable ticket rather than one that has to be fed into the barrier and retrieved, especially if you're a bit late.
Parking you usually get the saving on day five, so not worth it with them.
In a job a while ago, I worked Thu, Fri, Mon, Tue Wed in the office, over two weeks. Bought a weekly ticket on the Thu. Worked from home the other days. Halved my travel costs and was cheaper than a season ticket too.