Is it unwise to change my URL structure for future posts?

I have a blog and it is getting decent traffic. However, I’ve been reading a lot of SEO stuff lately and it seems my URL structure is terrible because it is a completely flat structure. I have categories on my site, but my URL for all posts is literally mydomain.com/post-name. I have read and listened to multiple sources saying I need to have my structure like mydomain.com/category/post-name. Would it negatively impact rankings if I move to the second structure for future posts but keep the first structure for my previously published articles that are already ranking? – by hq overview perribansheebones – –