[ECI-EN] RGB to CMYK for silk-screen printing

Hello, I'm a French visual artist working with silk-screen printing seeking for advice. When I convert my RGB files to CMYK, I lose a lot of color data and radiance. I use the Web coated swop 2006 profile to convert from RGB to CMYK. Which colorimetric profile should I use to reduce data loss during conversion? What about converting with a “multichannel” profile? Apparently it's also possible to use "Edit/Convert to profile/Custom CMYK", but I don't know what the values to be assigned correspond to. I work in 2, 3 or 4 color process using layer separation in Photoshop. I then recreate my CMYK manually by making my own inks. Sometimes modifying them. For example, I use fluorescent colors or a dark blue instead of a cyan.... Once the conversion is made, the CMYK profile that i use should thus be wide enough so that my simulations are as close as possible to the rendering I will get with my inks. Thank you for very much for your help