DIY a new chair
It seems as if every Youtuber has one of those fancy gaming chairs with headrests and speakers. They sure look comfortable, but also expensive. You must be PewDiPie to afford one of those to go in front of your computer. Don’t even bother looking at how much they cost.
Instead, you can be like this clever person here. Rather than splurging his savings on a new chair, he used a cheaper and more efficient solution. He put a pillow and pillowcase inside the back of the chair, resembling the expensive gaming chair he wanted. Instead of investing in a new chair, use things you already own. This is a quick and cheap solution for lumbar support.