1 gb ram and 2 gb of swap should be enough to get started. You can always do a server upgrade if traffic increases.
Any hosting you choose the basic requirement is that they support docker. The first hostings that comes to mind, in addition to DO, are Hetzner, OVH, Scaleway, UpCloud and Vultr but you can find more information here:
https://meta.discourse.org/t/the-cheapest-solution-for-hosting/24060
where you can also find some benchmark comparison