You can expense purchases that make your office or workspace a more suitable place to work. This includes essentials and some smaller decorative items.
You can expense the fit out of your workspace, so things like a desk, a chair, shelves, storage and other items required to work.
You can also expense smaller decorative items you use in your home office/workspace, a few plants and a lamp as examples.
Any stationery you use for your business is an allowable expense too.
If you undertake a larger redecoration project (say you want to repaint your home office), you won't be able to expense that. As a rule of thumb, any works that would increase the value of your home are unlikely allowable expenses