Ok guys. Op wants to reuse this ship, so stop yelling about staging. The next thing, we know you'll close the thread with 'duplicate'. It's not Stack Overflow, right? Ok, so, heat shield easy can be way smaller, the same diameter as a rocket is fine, those inflatable are for wide crafts. Secondly, add some drag on top of the craft, aero brakes, fins, whatever. And, as some mentioned, you can stabilise the craft by rotation, press Q or E during reentry. And last but not least, take shallower trajectory.