Hire an experienced (0-1) Product Designer and have them work out the features, design, system, interaction flow, and research. Test and validate you have the right thing before you start building. This can be done well in 6 weeks and it'll save years and years of debt.
Anywhere you'd find any other employee. Product designers aren't rare, it's just that immature development organizations usually use designers wrong. Bringing designers in at the end to add polish to the user's experience nearly guarantees they'll be polishing a turd. A big part of a designers value is figuring out what problem users need to solve with your software and what tools they need to do so.
