I have a pile of TP link antennas ive used for a bunch of stuff in the past that are pretty good but dont take that as an endorsement perse but really anything from a reputable brand should be fine. I'd probably avoid bargain basement antennas from china, QA can be super hit & miss there. If your feeling adventurous you can make your own antennas fairly easily and cheap too. Its also worth noting that its not guaranteed to solve your problems outright, there are other factors that come into play such as drivers, the bluetooth device your connecting to, noise, brick walls, antenna placement, etc that can also impact performance. It is, however, the cheapest way to likely solve this. Or to put it another way, its where I would start, a good antenna makes a world of difference.