Hmm, the train station thing would make me nervous! How long is the commute and how secure is the train station? If the answers are short and not very then I’d just get an old pooper, make sure it runs well and be done with it. I wouldn’t feel great about leaving anything worth more than about £100 at a train station, and even then it would be disguised to look worth a lot less.
If the answer is long and very, and you want to mix it up with some off road a touring/CX type bike might be good. Not a full on CX but something that’ll take mud guards and a rack. You’d also be surprised how much abuse a standard road bike can take, perhaps a steel framed (more comfortable than alu) second hand road bike with some sturdy wheels and 28-32c tires would be a good option.