Do you think I can change the site design myself? Can I do it well? I don’t really want to contact someone, order services. I’m worried that it’s not how I want it ..

Have you ever done this? Yes, try it! If it does not work out, you can always fix it. As I understand it, you do not have enough money. Do not worry, read the literature first, watch the videos, decide what you want and go for it!

I would not advise you to do this yourself. All the same, I attribute design to the area that should be addressed only to those people who understand this. Why can't you turn to professionals? I think if it is money, then you can always find what is available to you. And it will be no worse than something expensive. I can advise you a company that is professionally engaged in web design, if you like shopify themes then contact them and order a service. I assure you, the result will be exactly what you want!