It is an interesting question. DO + BE
You can use 'do' as an auxiliary with “be” to emphasize the imperative.
-Do be sure!
-Do be happy!
You can use "do" for emphasis with other linking verbs.
-I do seem sure.
-I do appear to be happy, don’t I?
But the emphatic 'do' is not normally used before the verb "to be" in standard modern English.
-I do be happy....not acceptable
-I do be sure......not acceptable
However, you could ask yourself a rhetorical question,
-Why don't I be sure first, before I act?
It is also possible to use do + be in the subjunctive.
-The boss insisted that I do be careful.
In some dialects, Irish English, Caribbean English, and American Black English “do” is used before “be” with a special meaning.
-I do be happy.....meaning.....I am usually happy.
-I do be going to McDonalds........meaning ....I regularly go to McDonalds.