Gel is unlikely. Gel pens tend to go through a lot of ink, so the refills are larger.

Pilot's Acro ink has a pretty good reputation. I believe that's the ink in these refills: https://www.amazon.com/Pilot-EasyTouch-Retractable-Ballpoint-Refills/dp/B00P2O81NC

If they're the right size, they might be a good option.