Choosing a business name and choosing a domain name can be fun but with literally thousands of possibilities, it can be exhausting deciding which one will make you the happiest in the future.
If you don’t have experience choosing a business name and a domain name, it’s worth spending 30 minutes or so reading other people’s advice. Spend more time until the common advice sinks in.
Ideally try to get the domain name to match the shortest version of your business name or product name and if that’s not available, you have to compromise.
Personally, I spend an hour or so brainstorming possible domain names and let my brain cogitate on the possibilities for a week or so and then try to make a decision. Try not to let the fear of someone else ordering a particular domain name before you rush you into to ordering it. The chances are very high that if it’s available now, it will be available next week.