To add to point #3 in Vietnhi Phuvan's response: you said that the new person's responsibilities will include mentoring and training you. This means that personal compatibility is very important: you want a person who you are comfortable being around, whose style of explanation you find easy to understand, who doesn't make you afraid to ask "stupid" questions, et cetera. It may even better to have a mentor with slightly worse technical skills but who you get better along with, than the other way around. All the technical knowledge in the world is useless if the other person can't make you learn it.
Because of this, it's very appropriate for you to be interviewing the candidates, because you're the best judge of how well you personally get along and communicate with someone else. Getting along with you is a vital requirement of the position that you've described, which makes you irreplaceable as an interviewer for this position.
This should also influence the way you choose your interview questions: for example, you could ask the candidates how they would explain some relevant concept to a person who has a basic technical background but isn't familiar with this particular part the domain. That will be a big part of what they will be doing with you, after all.
If you still feel uncomfortable, you can always just tell the candidates right in the beginning that they're probably more technically competent than you are, and that you're looking for someone who can teach you their skills. This also has the added benefit that you're lowering yourself from "scary authority figure who's conducting this interview and judging me" to "someone who respects me and hopes to learn from me", which may make the interviewees feel much more at ease. Job interviews tend to be stressful situations, and admitting your technical weaknesses may actually make the candidates feel more comfortable than if they thought you knew more than they did.