Hello
Good thinking on the travel part, although I would say most changing bags come with travel changing mats as standard.
Travel mattress may be an option?
Changing rucksack?
Or thinking ahead a little, travel bowls and spoons with waterproof bibs.
One friend got me a toiletry bag with mini travel versions of essentials. So thermometer, bath thermometer, baby shampoo, first aid kit, sun cream, teething gel, sudo cream, etc.
Or another favourite is a star wrap. Doubles as a blanket or snow suit and super cosy and portable.
Hope that helps a little.