What to add to make the car more stiff

Doing some research on mods for a (NA) to make it noticeably more stiff

So far I’ve read that these provide noticeable change:

• Frame Rail Braces
• Fender Braces
• Roll Bar
• Seam Welding

Have also read that these changes provide little to no impact:

• Front/Engine Strut Tower Brace
• Seatbelt Tower Brace

Anyone have any other input on this?

Am I missing something?

I’m not particularly knowledgeable and have been researching online to gather a detailed list to make decisions

Thank you