Firs of all you should quickly check free, responsive themes on wordpress.org. If there is nothing with nice layout and good functionality the next step will be to look in services which sell themes, like for instance in themeforest.net. The price would be roughly between $30 and $60. Themeforest.net enable live view of almost all themes and most often than not -themes designers provide very good support on the same website. There is no need to chase for theme creator to ask simple questions. For many WordPress themes there are available questions and answers concerning customization of themes, so it is possible that you will find answer for your question very quickly.
Rule of thumb is to pay for WordPress theme which is as close as possible to your needs. Try to find theme which will not require almost no code customization. Don’t assume, just looking briefly at theme, that modification of some layout or functionality feature will be quick and easy. Sometimes it is better (faster and cheaper) to modify your expectations than theme itself.
It seems that Web design is similar to football – everybody is expert in Web design. I am not expert, but what I have seen is that the less you try to modify WordPres theme, the less you will suffer. Anyway, why have you paid for this or that theme? You paid for it, because it looks very good. Do you think that affter your hammering-bettering customization, the same theme placed in online shop would draw your attention? Probably not. You BELIEVE that some specific heavy customization will benefit your online visitors or customers, but this is only your BELIEF but not KNOWLEDGE. To KNOW if modified functionality or layout produces better conversion you have to make tests, like split A/B tests, or some online surveys.
What I said above is true not only for normaln website owners, but for Web designers too. They like to use – to give simple example- very small font here and there, because it looks good. Maybe it looks good, but font as such is for text, and text is for reading. They forget that people will not only look at their state of art, but will try to read text as well. For this reason, the first and easy modification I recommend is to set the right font look and size.
Visitor’s patience has limits. If people have problems using your website, better replace theme with another one, with better usability and accessibility ratio. You will pay $30 – $60, but this will be one time payment and your conversion rate will stay improved forever.