Much of the area above Mürren is ski pistes, which you must avoid on foot. You need to look for the groomed walking trails, called Winter Wanderwege., to walk safely and in comfort. Here are some suggestions near Mürren:
https://mymuerren.ch/en/winter/see-do/#category60
More in the area, including from Wengen:
https://www.jungfrau.ch/en-gb/winter-hiking/
I believe the Männlichen to Kleine Scheidegg trail is groomed for winter walking. This you would access from Wengen by cablecar, then train down to Wengen after. Or from Grindelwald by gondola then train.
Be aware that the Swiss Alps just received a massive amount of snow, something like 6 feet over a short time. Train and car travel has been affected and people were stranded by lack of transport ( I.e. 13,000 people In Zermatt).
Your trip is still weeks away, but the excess snow conditions and avalanche danger may persist into your visit. Be sure to confirm the safety of any trails you choose before heading out.
It appears you haven't booked lodging yet? note that many hotels will have a minimum stay requirement during ski season, from 3-7 nights. For apartments, it is often a 7-night minimum.
One of many articles about the snow conditions:
http://www.bbc.com/news/world-europe-42623293