Anders from the Shopify Social Care team here. Thanks for reaching out.
I've had a chance to review over your site, and while admittedly I don't speak or read Dutch, the site looks great! Pages load quickly, it's easy to find products, and the checkout flow is quick and only requires a few clicks. If you're worried that your store's conversion rate isn't quite where it should be, I would first head to your 'Analytics' tab begin to review over a few reports to gain a better understanding of your customer behaviors. While each of these reports give their own beneficial insight, specifically, let's look at the "Online store by sessions by traffic source" and "Sales by traffic referrer".
Set the date ranges for these reports to 'last 30 days' and, given that you have been marketing online using paid ads (ie. Facebook, Google, Instagram), you can begin to nail down where your traffic is come from and what channels are specifically converting. Notice that there's not much traffic coming from Facebook, but it's converting into sales in the 'sales by traffic referrer'? Then I would consider setting up some more Facebook ad campaigns. Vice-versa if you notice the same with Google Ads or Instagram ads.
Now, while there is some commentary out there that email marketing is 'dead', simple campaigns like abandoned cart recovery and newsletter marketing can actually go a long way. The great thing about a solid email campaign, as well, is that it can largely be automated. In fact, we have a great article which covers 7 different ways you can build an automated email campaign. You already have a very slick looking website, so a bit of ad re-targeting and expanding your marketing methods should lead to some good conversion numbers!