I think it's definitely worth talking to your GP and getting a referral to a GIC, I've been told to expect 2 years for my first appointment. It varies depending on area but you can cancel before your appointment is close if you change your mind and they will fill it easily.
If you can afford it visiting a private gender therapist is extremely worthwhile, I did some therapy before talking to a doctor. Also, I would be surprised if many people are 100% certain when they start, I've only just started HRT but it wasn't until I experienced that that I was sure it was the right path for me.