Sure, in my opinion, Keyword + Number is a good combination.
ESPECIALLY, if the number is 1 (one), then, it has more value than any other number.
travel1.com can be a top brand name.
travel0.com - To be avoided. Zero has both pros and cons.
Pros: zero means free.
Cons: zero means no profit!
Besides it can be confused with travelO.com. The 0 (zero) can be replaced with O (letter) and there is potential for phishing websites to exploit the audience. If someone is putting a zero cost service then name with 0 has some value, otherwise, it should be avoided as a brand. I wouldn't hesitate to launch a brand with 0 in the domain name, if it makes sense!