Doppler jelly help!

Alyssa

I bought a Doppler from a child resale shop a while back knowing we’d be trying for #2 soon. Well I’m now 4 weeks pregnant and know it will be awhile until I can pick up the heartbeat but the Doppler I got does not have any jelly. So I wanted to know what your favorite jelly is so I can research and get some ordered for when I’m far enough along.