I've people that are ready to buy but I don't know how to administrate it to be attractive and easy to pay for these people.
Should I send an email with all preferences to answer, or a email that is attractive for people to click and then a webpage with preferences and payment ?
A specific solution just came to mind utilizing wooCommerce. If WordPress is your platform, this could be very simple with a subscriptions plugin.
If you already have people willing to subscribe to the service, best thing is to activate them with a "Welcome" email with a link where they can enter their preferences, billing and and shipping information in a single step.
Happy to talk through specifics in a call.
lesser the steps the easier your customers would feel and higher their willing to purchase would be, if u the make the process difficult then it would be a turn down for your customers. If you can share further details, i might be able to answer in much better way, thanks :)
I have experience in this field actually. I was co-founder of a high quality feminine napkin company, Empower Pads, where we used a green homeopathic strip which helped women with things like ICT, urinary tract infections, cramps, etc. (http://icnetwork.empowerpads.com/)
We never did sell a monthly subscription though, we went to a lot of trade shows and tried some JVs with custom online sales pages like the one above.
In the end we found that the product was too difficult for us to move because people don't like to talk about pads and tampons. Its not really a big 'referral' product. It helped thousands of women, we got hundreds of amazing video and written testimonials & reviews, but it didn't take off for us.
You could look into the product Poo-Pourri (http://www.poopourri.com/) and see how they created a viral video campaign for a similarly difficult product to market. Their video and sales page spread by using comedy to sell something that people don't feel comfortable talking about.
Another good monthly sales subscription to look at in the personal & grooming space is Dollar Shave Club (https://ca.dollarshaveclub.com/). Although it's not extremely relevant to tampons & pads because men don't have a problem talking about razors.
You could also try sponsoring podcasts with similar interests.
Hope that helps.