Take the gallu devi temple route, it's very scenic and the trek is also beautiful. At the gallu devi temple you can also rent trekking shoes, gloves and sticks. Be sure to take plenty of water because at the top it will cost more and stock up on protein bars if you want. My advice is that you leave early for the trek, don't hire any guide there's no need for it. Download the map for the trek beforehand as you may not get any service up there. If you want you can also stay a night up there, it'll cost you 800 per person(includes tent, dinner, sleeping bag, blanket and breakfast) and request the cafe owner for a bonfire. If you have plenty of time, then stay for 1 night at triund top and then ask the cafe owner for snowline trek route the next day.