WooCommerce is designed to work well within whichever WordPress theme you are already using. Dedicated WooCommerce themes, however, will have options and styles specifically for WooCommerce stores.
You may want to try out different themes to see which you like best. The recommended default theme for WooCommerce is called Storefront.
What to Look For in the Themes Marketplace
When searching for themes you can be as specific as you want as far as styles and options. You can also choose among Free themes and Premium themes.
If you are in the market for premium themes you can spend between $75 to $200 or more. Before you spend money on a theme you should make sure you trust the developer, the theme is highly rated, and the theme will be supported through later versions of WooCommerce and WordPress.
Working with Mobile Themes
Some themes offer both a desktop layout and a mobile layout in the same package. This saves development time.
The desktop layout will typically be optimized for wider desktop monitors. The mobile layouts will fit more information into smaller screens for increased readability on tablets and phones.
Check your Theme Options under the Appearance tab for more information on your theme's customization options. The default "Storefront" theme has desktop and mobile layouts.