Three quick points:
A. Alan, yes, it sounds like you have amplification of sufficient quality to enjoy your melodica and focus on the music and practicing. I find myself continuously distracted by technology or searching for nuances in sound. That is a bad thing and I must focus more on the music myself. I did not intend to imply you need additional amplification, but was rather sharing some first hand experience about amplification in general.
B. Don’t overlook backing tracks on YouTube as an inexpensive way to play along with good musicians and play a variety of music. There are hundreds of tracks in the blues and reggae genres, and no doubt there are jazz backing tracks too. Most are very good, some are not. You need to be selective.
C. As Melodica-Me mentions, Jamey Abersold has some wonderful educational tools for jazzers. But he also taught me in a two-day seminar I took with him, that if you really want to get people excited about music and get them involved in playing, have them create their own music. Creating original music is wildly fun. Just start simple. Great music does not have to be complicated.