Another option is the Gevenalle brake/shifters.
https://www.gevenalle.com/product/cx2/ I'm not positive but I believe you can mount your current 8sp shift levers to these saving you from having to buy another cassette or just get the 9 or 10sp if you're planning on replacing your current cassette. Contact Gevenalle to be sure. There are demonstration videos on their website showing how they work.