Can I buy a new iPad which will use the same charger as my iPhone 12s and my older iPads?

You would be better advised to consider using your new USB-C Power Adapter which has a higher power output - and supports fast charging with compatible devices - and instead invest in a USB-C to Lightning cable to charge your iPhone and older model iPads.

• USB-C to Lightning Cable (1m)

https://store.apple.com/uk/xc/product/MM0A3ZM/A

• USB-C to Lightning Cable (2m)

https://store.apple.com/uk/xc/product/MQGH2ZM/A

The iPad Pro, iPad Air, iPad mini, and iPad 10th generation all have USB-C connections for charging.

The only model currently sold that has a Lightning connection like your iPhones and older iPads is the iPad 9th generation.

Also see: iPad - Apple