I agree with @steveridout on the name. It’s on the fun/playful side, more personal than corporate, and it connotes the beginning of something. If that’s what you’re aiming for, I think it sounds good.
On another note, and I think this is more of an issue once you’ve got some early adopters, is that different audiences will react differently to non-.com domains. So if you’re targeting developers or startup folks, .io is great and you could stick with that for a while. I’m not sure who your customer base would consist of, but I’d think non-technical general population consumers and financial types would be more wary of a .io domain. That’s not to say you shouldn’t start out with that name, since wasting time trying to find the perfect .com is probably not worth it, but you might want to just keep that in mind as you’re doing your branding.
Btw, when I search for “Sproutly” in Google I get a top hit of Sproutly.com (I’m sure you’ve already done this!). This is someone’s personal blog, but it looks like it hasn’t been updated in a while (couldn’t find a date, but the last comment on the second article from the top is from years ago).
This might mean you could buy it out from them, and if you’re serious about the name I would reach out to them, explain your situation, and offer a small amount of money for it. I don’t know your financial situation or how much you have to offer, but I’ve bought domains from real (non-domain-squatter) people for around $100-$200 before. If they say yes, then great, you’ve got a .com. If they tell you they are passionate about the name and would never even consider selling it, you might want to think about a different brand name.
Just my 2 cents.