You can connect as many domains as your plan allows and pay for them from one account.
If you are looking for a new domain, you can read one of these articles:
Remember that the best way of creating and sharing links is in the usage of your own branded domain, not the common ones.
The number of domains you can connect to your account is limited and depends on your plan. As an option, you can register “tiny” plan account and join up to 3 domains for free (in purpose of review) and then upgrade your plan for affordable price. To choose the best plan for you or your company you can visit price section.