I will not waver

I’m looking for another way of expressing the statement

I will not waver.

I have looked up synonyms for the word certain, but they just do not seem to fit into what I’m composing.

Solution 1:

You say, "I have looked up synonyms for the word certain." This means that you are looking for a positive expression of the phrase I will not waiver.

I would use:

I will remain steadfast.

From Merriam-Webster:

1 a : firmly fixed in place : IMMOVAVABLE
b : not subject to change
the steadfast doctrine of original sin
—Ellen Glasgow 2 : firm in belief, determination, or adherence : LOYAL
her followers have remained steadfast