Not to go into too much detail- I have a hearing deficiency wherein I have trouble hearing the pitch of my own unamplified voice. I've heard recordings of my voice which makes me cringe because I can't believe how pitchy it is. Of course in front of a microphone I speak and sing well enough. I'm a classically trained bass player and have a good sense of intonation, but I can't train my voice properly if I can't hear it well!

so... any tips on how to hear my own unamplified voice better? (hearing aids, techniques, etc...)

What you are asking is basically a medical question; I suppose you have gone through the specialists and they may have (or not) technical aids to help in alleviating your condition.

In case you haven't, I can only tell you hearing aids could help, maybe a bone transmission model as you may be most interested in the bass register, while in-channel, eardrum based transducers (being very small) should lose efficiency at lower frequencies.

I suppose you understand that a heavy hearing loss condition is an important handicap for a singer. As you say you are a trainer singer, I assume the problem showed up after you started your career; it is very brave from your part to decide to continue this career (and it is encouraging to others that may be noting a progressive hearing problem, as myself) but the way can be difficult.

You should seek very specialized medical advise (in case you haven't so far). Depending on the cause as is the case with middle ear problems, surgery can help, but I am afraid the results are, sometimes, not much reliable.

If you are proposed to have a prosthesis implanted in your middle ear, be very careful and do a lot of research and consulting with several specialists, before proceeding. And never allow to have both ears operated at the same time.

Inner ear problems can be far more difficult to treat and the results could be useless for a singer, though they could mean an important improvement for a completely deaf person.

In any case I wish you lots of good luck.

<Added>

OOPS!
trainer singer = trained singer