When you can afford it, I would hire a UX designer with a strong portfolio of usable/accessible design projects that knows how to interpret behavioral analytics into improving the UX over time as the company adds new features.
If you can spend money on marketing, you cannot afford to not spend money on ensuring the UX is working for your users and to get insight into if poor design is the reason behind not performing as expected for your bottom line.
Pro-tip: UX is NOT UI (there are a lot of off the shelf design systems that make designing UI trivial e.g. Salesforce lightning design system, material design, etc. - hire someone who is a UX design generalist until you can afford specialists - UX designers/researchers).
If you can spend money on marketing, you cannot afford to not spend money on ensuring the UX is working for your users and to get insight into if poor design is the reason behind not performing as expected for your bottom line.
Pro-tip: UX is NOT UI (there are a lot of off the shelf design systems that make designing UI trivial e.g. Salesforce lightning design system, material design, etc. - hire someone who is a UX design generalist until you can afford specialists - UX designers/researchers).