Heya,
Some big umbrellas with some bounced flash can be very nice. Depends on your desired result.
Depending on budget, I'd consider something like:
Yongnuo 560 III's (get several). They're wireless built in, manual flashes. Great values. Command a fleet of them with a Yongnuo 560-TX (it can control all the power levels of the 560 III's from that one controller; no need to buy any transceivers at all, these have it all built in). Simple, portable, inexpensive, and lots of light. Less components, so less batteries and less hassle. But, the compromise is that it's manual, so you have to adjust the light yourself. Tweak it to your exposure and then shoot away. Bouncing from modifiers like umbrellas would be great.
Otherwise, you could supplement your current flash with some Yongnuo 565EX II's, which have ETTL. Then, get some YN622 transceivers that handle ETTL wirelessly. Instant auto-exposure. Set up a few of them and bounce the light off modifiers (like umbrellas).
Get a few inexpensive light stands that can hold umbrellas, and I really recommend S-type brackets for holding umbrellas for now. Sure you could just get cheaper mounts that only hold umbrellas. But the S-types can hold an umbrella and be fitted to a softbox for future work (especially for jewelry and other stuff where you want close range, soft light). Example of a S-type mount.
Some huge umbrellas would be good. Something like 43" to 60+". You can use silver to maximize the light bounce and contrast. Or you can go with white and just go for a softer more diffused look. You can get umbrellas that have covers so you can do both with a sleeve. I'd more likely go for silver umbrellas here. The other option is big softboxes.
Example of a big softbox for cheap, that speedlites can be used with.
Food for thought.
Very best,