I use some not-as-smart smart bulbs that allow me to use all sorts of FOSS alternatives to control them which I only lucked out into getting since I was planning on getting Philips Hue, but these that I got (Wiz iirc; I don't use the official software so I am not constsntly reminded of the brand) were half as expensive so I was able to get more of 'em.

Home Assistant is entirely self-hosted. No third-party required. It can run in a container or on a raspberry pi, but it’s typically easiest (and most functional) when you use a dedicated Home Assistant Green. It connects to Zigbee, Matter, etc via USB adapters. Or if your devices are networked (instead of using a hub), it can often find them directly on your network via local device discovery. It integrates with Alexa really well, so you wouldn’t need to immediately ditch your existing smart speakers.

If you really want to get fancy, you can even set up a local machine to do local LLM processing for self-hosted smart speakers.

I personally started using it after my smart light provider (Sengled) had a few extended outages. There was no communication from the company, and lots of people were speculating that they had gone kaput. It was literally cheaper to just get the HA Green and a Zigbee dongle, and set that up (instead of replacing all of my lights with a different brand). And since it’s entirely self-hosted, it even keeps working when my internet goes out during storms.