Since your central question seems to be about the general case ("How do I translate reflexive first person"), here is a more general answer that builds on the above suggestions: A simple me is all that is necessary, but there are ways to emphasize the reflexive pronoun if you wish.
One way, given by Joonas, is to use ipse.
- You can append ipsum after me:
Ergo ista, inquit Crassus, quae habes a me, non reprehendo, ne me ipsum inrideam. (Cicero, De Oratore 3.47)
Crassus said: "Therefore I do not blame you for those things which you have received from me, lest I make a mockery of myself."
- You can also use ipse, agreeing with the understood ego.
sed non egeo medicina, me ipse consolor (Cicero, Laelius de Amicitia 10.10)
But I have no need of medicine: I can comfort myself.
You can also use an emphatic -met at the end of the pronoun:
neque, ita me di ament, credebam primo mihimet Sosiae,
donec Sosia illic egomet fecit sibi uti crederem. (Plautus, Amphitruo II.i)
Nor, by all that is good and holy, did I believe myself, Sosia, at first
until Sosia made it so that I believed him.
(It's difficult to translate this passage out of its context: Mercury takes on the appearance of Sosia, a slave, and manages to convince Sosia that he is the real Sosia: I recommend the play!)
You can just use me alone if you don't feel a need to emphasize the reflexivity.
ubi ille ábiit, ego me deorsum duco de arbore. (Plautus, Aulularia IV.viii)
When he left, I let myself down from the tree.
The point is that Latin only has a special reflexive pronoun for the third-person: you can use me regardless of the subject. In fact, all the "emphatic methods" above could be used just as easily if it was not reflexive.
For your actual quote, my translation agrees substantially with Joonas's, though adsentior sounds better to my ear:
Non semper mihi adsentior.
Non semper mihimet adsentior.
Non semper mihi ipse adsentior.
Non semper mihi ipsi adsentior.