Where can I find winter wear such as winter boot & coat, leather glove at cheap price in Beijing?

As I know, Yashow Market is nearly closed. You can go to Guanyuan Wholesale Market in Chegongzhuang Avenue, Xicheng District.

Is it better than Xidan Commercial Street?

I have two places to choose to stay, either Happy Dragon Backpackers Hostel or Party Youth Hostel. Which one is better and how to go to both hostel?

Generally, it’s cheaper to shop in Guanyuan, but there are more choices in Xidan.
As for the two hotels, I suppose your departure place is the capital airport?
If so, to Happy Dragon Backpackers Hostel: take shuttle bus line 13 to Huaqiao Dasha, and then walk north for about 5 minutes there.
To Party Youth Hostel: take airport express and transfer to metro line 2 at Dongzhimen. Get off at Gulou Dajie and leave from Exit A2, and then walk north for about 1.2km to the hotel.