Pull everything out. You can’t judge it if you can’t see it. And who knows what you might find - discovering an old forgotten favourite is like getting something brand new. But free!
If you are lucky enough to have a designated office then shut the door and go be somewhere else. If you are working on your kitchen table then do an exercise video, meditate, lie on your back in the dark for 10 minutes, phone a friend. Just something that means the work portion of the day is clearly ended.
An alterations tailor can be a wizard or a headache so do a bit of research and find a decent one. It is worth paying a premium for a job done well. I have fixed so many botched alterations over the years which means the client has ended up paying twice! Buy well. Buy once.
The cloth you choose will also slightly determine how you can wear it. A high-cut 3 button jacket in a warm tweed can be a really smart alternative to an overcoat. Alternatively, a navy worsted will be more Pierce Brosnan era Bond. Both very cool, but very different looks.