[Lazare]

> I’m using sessions/cookies for keeping state and keeping the user logged in

Good. Sessions are the standard for a reason, and it's currently considered best practice. And if you've got a session ID, and your clients support cookies, then sure, use cookies for storing them.

> will using JWT (with the token stored in the cookie) to keep the user logged in instead of sessions/cookies make my application more secure

No. Probably less secure, although if you know what you're doing you can mitigate the issues. But certainly not more secure.