When I design a simple postcard in Photoshop and use one of my photos, I'm not sure what color space or how to save the file so that it won't change the color of the image. When I use CYMK it turns the photos I use neon and RGB looks like someone unsaturated the file.
For an end-user inkjet printer, use RGB colors.
For a commercial printing press use CMYK colors.
If colors are not accurate when printed, calibrate your devices.
Without more information with respect to the actual printing process you are using (equipment), this is the best I can provide.
Don't use your monitor profile as your colour space. At minimum use your intended output space - sRGB for web, etc. Your monitor profile should appear in the list of potential spaces, but never select it for your Working Space.
As this seems to be something of a contentious issue [see comments], let me refer to Adobe's own colour workflow documentation - https://www.adobe.com/digitalimag/pdfs/color_managed_raw_workflow.pdf
Note: most 'consumer' printing facilities prefer sRGB even though the result will be ink-printed, which in 'pro' terms would need CMYK.
...another 'not really an answer' but based on current question & lack of real detail