The only other freeish solution I can think of would be to flash custom firmware onto the switches. The problem there is that apparently these are a pain to take apart and soldering/desoldering is involved. As for the firmware, Tasmota might work, but I really have no experience with it and can’t say for sure.
Link to discussion on flashing: https://github.com/arendst/Tasmota/issues/4003
Tasmota integration with SmartThings: https://community.smartthings.com/t/release-tasmota-connect-for-sonoff-tuya-smartlife-other-esp8266-devices/187553
If you are willing to spend a little money, I’m fond of TP-Link’s Kasa switches. They are now compatible with SmartThings and have been working great for me.