Mom has lived with us 18 years. She is 98-years-old. She has dementia, is wheelchair bound, needs help toileting (she is incontinent), giving her meds, meal prep, occasional wound care (ostomy bag). Transferring from wheelchair to recliner. I am her caregiver and need someone for only about one time a month for 8 hours/give or take. It could grow and vary. Every agency that I have called wants clients who can commit to having a respite caregiver on a weekly basis for a minimum of 6 hours per week.
Once you have this going, I think you’ll find that your own life is so much better as you can schedule your own activities - your dental and medical visits, your hairdresser, your own personal time (yoga, aerobics, pedicure, retail therapy) - as it gives you a way to be ready for a time once mom is not longer there. 18 years is…. Like a whole childhood but in reverse, it’s going to be quite an adjustment for you and your household.
The caregiver is there for mom but it will be of benefit for you as well.
It would have to be the same time and same date every month though. No agency is going to keep someone on call for a monthly client who's days and hours change.
If I were you, I'd hire a private-duty CNA to come and work in cash once a month. If your mother needs meds given and ostomy care that is not the kind of care a homecare agency companion does and no agency sends a CNA for 8-hours at a time.
Look on a caregiver website like care.com for a private CNA who will do one 8-hour shift a month. You will need an experienced one. If it's a private hire you'll looking at between about $20 to $33 an hour depending on where you are.