People are going to talk about lined vs unlined fingerboards. Full disclosure: I play lined fretless,
but I prefer the look of unlined. You can absolutely start off on fretless, but I would highly recommend you pick up a cheap, lined, fretless, for two reasons: 1. the lines can help you find the correction positions (bear in mind they are guides, not absolutes, and your ears must guide you to correct intonation), and 2. if you decide fretless isn't really for you you're not out a lot of money on bass you don't enjoy playing.
Fretless is an absolute blast. With good technique you can sound like you're playing a fretted bass, or you can slip and slide and mwah to your heart's content.
Lessons are always a great idea.