I recommend getting a nice set of watercolor brushes for paint and inks.
Aim for natural hairs, sable when possible.
They hold the pigment and water better. If sable brushes are too pricey for you, then start with some bamboo handled calligraphy brushes. They are wonderfully versatile for line and broad stroke applications alike.
Hint: Visit your local Chinatown… there are lots of inexpensive and very high-end brushes too.
Please take good care of these brushes. Always wash them in warm water with mild dish soap and hand them bristle side down to dry. This will keep the glue from washing out and losing your bristles. Do not leave them soaking in water for too long, if at all. Use them mainly for calligraphy strokes or washes, not to grind-blend.
I’ve had some brushes for more than 30 years because of this loving care.