Hi Shadi!
If you are going to Osaka. DEFINITELY VISIT SPA WORLD!!
But here's a handy recommendation guide for each city:
Top 10 Best hot springs in Osaka and near Kyoto .
https://planetyze.com/en/japan/osaka/blog/top-10-best-hot-springs-in-osaka
Top 10 Best Hotsprings (Onsen) Around Tokyo
https://triplelights.com/blog/top-10-best-hotsprings-on-1811
I Hope this helps!