If you see a green bubble (with a number in it) on the menu button (3 horizontal bars top right), tap on the button.
You should then see a Bell (notification) button on the popup.
Tapping on the bell will pop a list of notification links. These will include responses to your thread.
As to your question, the single rate is quite variable.
Some cruise lines offer single occupancy cabins on particular ships.
The default for regular cabins on mass market lines is usually twice the single person fare in double occupancy, sometimes less fees and taxes. In other words, the advertised fare times two.
If you haven't already, check out the single cruisers section of CC, https://www.cruisecritic.com/hub/singles-cruises/.