YWCA is a good option to start off your trip in Kerala. Unfortunately they do not have any on-line reservation.
They can be contacted on:
M.G. Road, Thiruvananthapuram, Kerala, India.
I am really sorry I dont have their phone no, nor is one available by searching on the Internet.
On-line reservation is available for several other hotels, try the web-site - www.hotelskerala.com
. I think there is on line reservation for YMCA, (on this very site) perhaps if you could send an email to YMCA and ask for details of YWCA they may oblige.
I generally check in at YWCA, whenever i travel, even if for a day, collect details of safe places to stay in other areas of the same district and move on.
Kerala, I hear is a safe place, though i have not visited it yet.
Have a nice trip.