As a first Snake, I would recommend a Stimson Python or a Childrens Python. Both of these Snakes are very gentle and grow to about 1.2m, they live for a long time so you will need to make sure that you are willing to keep them for a while. Always get a Hatchling for a first snake, remember though, all hatchlings are a bit snappy until they grow a little. I guess it is because they are so small and they have a strong self preservation instinct until they know you and see your not a threat. A bite from a hatchling is nothing but the speed they can move is a bit unsettling but the bite doesn't hurt. I started with one Stimson and I now have 5 Pythons and love them dearly.
One piece of advice, start with a small enclosure or tub for a hatchling. As they grow you will need to get a bigger enclosure and then their final home. Snakes can get stressed if they go into a big enclosure, they need a small area that they can coil up into a ball and feel safe. Lizards aren't like that but Snakes are and you will have a happier and friendlier animal.