Delhi to Trivandrum route via trains?

andicodesign

Hi everyone, I guess everything is global these days. What would we do without the net?
Here's my first post and apart from a short holiday on a Goa beach, it's my first trip to India.Late Jan to early March.
I have booked a flight to Delhi and 5 weeks later a flight home to the Uk and eventually Wales ( which is the best country in the world!And me an Englishman!)from Trivandrum.There is so much information out there and I'd welcome a recommended route to be able to take in the culture, have a good time talking and eating and ending up being hooked on India!I don't want to rush around. I can handle hassle but would love my time to be reasonably laid back, is that possible? The one thing I really can't fathom either is whether to get a pass for the train or just buy tickets. I have to confess even though I have read some of the books I still don't know what the benefit is of an Indrail pass is unless it is all about opening doors a bit wider?