What do you call someone who supports others by checking in with them when they're trying to achieve a goal? Not a sponsor.
advocate, ad·vo·cate \ˈad-və-kət, -ˌkāt\ noun –MW
3: one that supports or promotes the interests of another
If my lab partner wasn't such a good advocate, I'd have failed physics.
Are you looking for "patron"?
- One that supports, protects, or champions someone or something, such as an institution, event, or cause; a benefactor: a patron of the arts. TFD
"Lorenzo De Medici is said to have been a patron of the arts."
"John has found a patron in Dr. Cole."
I think "coach" may fit here. Coaching has by nature a 'caring' and personal quality to it. The coach or person checking-in must be somehow invested in the other persons success. Their success is the coach's success. Being willing to be supportive in this way (with regular check-ins) requires somewhat of a parental outlook. They agree to be caring enough to be a (however) constant in that persons life. This requires commitment from both the coach and the coached, thus the inevitable personal aspect of the relationship.
The way I find "just the right word" to use is, I start with whatever word I first think of, even if I know it's the wrong one (like 'sponsor'). I use either Thesaurus or dictionary to find its synonyms. And I just go from there, checking out the words and definitions and as I get closer, the context in which they are used until I'm satisfied I have the right word to express my thought. Good luck