Hi,
If you want to accept credit cards on your website with the credit card form on your checkout, you will indeed need a SSL certificate on your website (and make sure that your website is PCI-DSS compliant.
But you can also accept credit cards on your website with a credit card form on an external site after the checkout. Do you know that PayPal already offers the possibility for your customers to pay by credit card ? So in that case, it would actually be something you already have. Nevertheless, yes, you can use another payment gateway in order to offer credit card payments on your website. It could be an international one like CardSave or 2Checkout (for which payment plugins exist for HikaShop) or it could be one provided by your bank (in which case there might or might not be a payment plugin). So you could contact your bank and ask them what payment gateway they support for online sales and see if a payment plugin exist for it. Usually, your bank will have lower fees than PayPal which can be quite interesting.