Did you look into this Nickyy? A quick google of 'clipping path services' brings up loads of them, apparently starting from under 50p per image for a basic cut-out! That is the full extend of my knowledge, other than to say these services are very popular with on-line sellers facing the same problems as yourself.
But I can't help thinking that, particularly with your line of quality products, some fundamentally better photography would enhance your business. Attractive images that show colour, shape and texture accurately would surely both increase sales and save costs in reduced returns.
We're all reading between the lines of your posts and no doubt coming to some wrong conclusions, but here's another line of thinking. Get a better camera and a couple of studio flash heads (starting under £100) with softboxes. Concentrate on lighting the dresses (we've hardly touched on that yet) and pretty much ignore the background - with a white backdrop quite close behind it'll come out light grey anyway so that a fast and affordable cut-out service can easily sort it to white.
I understand your frustration that things are not as easy or straightforward as you imagine, but that's a common mistake. Smartphones have given everyone the impression that photography today is just a matter of pressing the button. But we're not talking selfies here, snapped on a nice sunny day - that's easy, they're just 'recording' a subject that's already in front of the camera and in God's good light. What you're needing to do is both 'create' the subject in the first place, and then light it properly - totally different. And white backgrounds are notoriously tricky as they have to be treated as a separate subject, plus there's the main subject, and then the two must be carefully balanced together - so that's three challenges for starters.
Please don't take this the wrong way, but your question is a bit like asking what saucepans are needed to cook a resturant quality dinner, when you don't have a kitchen, no recipe or ingredients, and have never cooked anything apart from a microwave meal before