Used handlebar bags to store extra bottles... didn't like it. Took away handlebar space.
Didn't bother with waist hydration belt. Sweat drips to your lower back so it gets mushy there.
Tried mountain bike hydration pack, overkill and too much storage. Still use the pack for mountain biking though, it (Osprey Raptor 15) doesn't work very well for hunched over position on a road bike.
The closest I found that works is running hydration vest with minimal storage (5 to 10 liters), and put a 2L hydration bladder in the back and wear it like a vest.
I have this:
https://www.aliexpress.com/item/33026101954.html Very flexible fabric. It has front flex bottle pockets to put 2 500mL flex bottles to extent the water capacity to 3L. You'll need to supply your own 2L bladder.