Technical consultant for E-commerce website and sust

We are in e-commerce apparel business. We’ve been in business for over 10 years. But we started out quite small and weren’t expecting the business to grow as much as it has. So the system and the website is not optimal for the growth and scaling that we have experienced, and that we expect in the future.
We are looking for someone who is experienced with working with big companies, that can help us create a better, elegant, more efficient system.
Someone who knows much more than us about what we could improve in our current system, and would know how to make it happen.
Someone who really has an advanced level of expertise.