Everything can be found online these days. I personally use Travel Joy or AIG Chartis as I find the price reasonable and the coverage to be within my needs. All you got to do is google for these (and NTUC and whatever other company that you can think of or is recommended) and you will be able to get a quote online. Just key in your days of travel and the region of travel (all websites are self explanatory) and the system will calculate the costs for you. All terms and conditions are listed on the website so that you know what you are getting before you buy it. You can always make a comparison of all the different insurance policy and decide for yourself which one suits you best, which is what I do all the time. If you are too lazy to DIY or find it too troublesome or you cannot make head or tail of what the policies mean, then give your insurance agent a call and get him or her to check things out for you and explain things in details to you.
To get insurance or not for your travel is up to everyone's own discretion. Some say yes, some say don't waste money. At the end of the day, just remember, the money comes from you and the protection is for yourself. Insurance, if you have not figure it out by now, means protection for unforseen circumstances or accidents. The key words are "unforseen circumstances" and "accidents", meaning things that happen without anyone being able to predict it. Judge for yourself whether you need it or not.
No. I am not an insurance agent. I just travel a lot and pose myself this travel insurance question all the time.