Can it be done? I recently started doing some writing in first person. I find it natural for descriptions of things that happened to be in past tense, but when talking to the camera, I slip into present. Teach me the ways. How do you feel about that? Example: They had done this thing, but we kept it going. Doing is hard. I like to think we tried.
That's close to how I speak casually. I often forego proper tense. Could work well for characterization, but it might be difficult to read if it's the bulk of the prose.
This can be fine. It depends on where your narrator is placed in time, relative to the story. This sounds like your narrator is somewhere well past at least the current part of the story. And it also assumes that the activity described by "doing" is one that still exists, and is still hard, in the place where the narrator is speaking.
I always struggled with this when writing in first-person, but my current WiP is in third and I just don't have the same hang-ups. In third I'm perfectly happy to use 'now' and 'tomorrow' in the narrative - not exactly switching to present, I know, but I would never have allowed the use of these adjectives if I'd been writing in first-person. Explain that to me, someone.
I'm dyslexic. POV triggers my dyslexia so badly I can't even tell you which terminology is correct for the POV I'm using in any of my work, no matter how many times the differences are explained to me. Somehow, I get it done by writing by instinct, with these two rules for myself: 1. Be consistent. 2. "Can this character or narrator know this?" Stick to only what that character or narrator would know at that point in time. ETA: You can slip back and forth, BUT Rule #2 is iron clad. (I also work closely with my alpha reader, but she adheres to the above two rules when looking for inconsistencies.) I think with practice, it really does become instinctive. Hang in there!