How long does the effect of fillers last? I have a lot of questions since it's my first time.

Lately, my face seems to look a bit flat overall, so I am looking into filler treatments. In particular, my nasolabial folds appear deeper than before, and I am especially self-conscious about that area when I take photos. Since this is my first time getting fillers, I am looking for a natural improvement rather than a dramatic, unnatural change. However, opinions regarding the duration of the effects vary from clinic to clinic and review to review, so I am curious about exactly how long fillers last. I know that it varies from person to person, but do factors like the treatment area or the type of product also affect the duration? If the effects are short-lived, I worry that I will have to get them redone more often than expected, so I am also concerned about the cost. For those who are looking into fillers for the first time, I am curious to know what questions you asked during your consultations. Also, please share any criteria I can refer to when choosing a treatment area or product, taking the duration of the filler's effects into account.