House plants, rugs, lamps and wall art go a long way towards making stuff look more adult-like and "complete".
As far as amenities go, a space heater is pretty meh and they cause a fair amount of house fires. Don't recommend it. Someone said heating blanket which I will second if you're trying to save cash.
Rice cookers are great, but honestly rice isn't that hard in a pot so I would prioritize other stuff first.
Bidets are life changing, and they help save on toilet paper which is nice.
The French press is a really cheap purchase for making coffee and quite versatile.