A couple of comments here... Google "merchant account reviews" and you;ll come across a few sites that tell you about the many different merchant accounts available, including their rates, their startup fees and if they have restrictions. This should help you in your research. I found mine this way, and have been very happy with it.
Authorize.net is a gateway used by many merchant accounts in order to process sales "realtime", meaning that the the credit card is charged immediately (same as Paypal usage). You can also process sales offline (meaning process the cards manually) until your business builds to a point where you can`t keep up with the manual processing and need to have realtime processing. There are merchant accounts that offer Authorize.net service free as part of their package, so this is something you will want to look into as well.
CardServiceInternational has been out there online for years--I recall using it some years back for a client, but it also started as a gateway (online at least) and has apparently moved into offering merchant accounts due to the profitability. Both CardService and Authorize.net are more expensive due to their longevity, perceived trust value, and so on... they may be where you want to go once you have a business built up, or as a gateway as part of another merchant account, but I do recommend that you shop around for merchant accounts and read all the reviews you can before making a decision.
To some extent I understand why the merchant accounts are a little leery when it comes to lingerie--it`s perceived as an adult item, which the pictures on your site tend to support (but they`re the kind of photos that sell, so...). Adult items carry more risk, particularly of chargebacks, so the company is trying to cover that risk for themselves since chargebacks are costly to all. Talk to the merchant account companies and see if you can`t get their rates down--talking to a real person is often the route to get better terms on your account. And ask if there are policies you can put into place that would help get those merchant rates down, in the end this will be of benefit to you as well, as you`ll see fewer chargebacks (for those who are unfamiliar with the term chargeback, this is another word for "returns", but from the merchant end).
In terms of your site, the opening screen is awful in Firefox--it shows as a small thumbnail at the top of the screen, and while it "works" in terms of being able to click a link, one needs a magnifying glass to see those links at all. The cart part of it is okay, if one can figure out how to get to it... except for the images.
The images issue is caused by the cart itself--it`s resizing the images to fit, and the resizing is distorting everything. The designer needs to find out what the default size of the images should be, then match the images to that sizing. You may be able to adjust the sizing in the cart itself so that some of this is unnecessary, but all the carts I`ve ever used require a maximum image size for thumbnails and for detail display, and these limits need to be observed or you get what you see on your site. Also check for spelling errors, I came across at least one on quick observation: under Romantic Lingerie, the top one has the word "mathing" and not "matching"... so maybe we`re doing a little addition with the lingerie?
Hopefully this will help you in your search....