I’m sorry for your loss.
Yes it is absolutely fine for a boar to live with one sow. I wouldn’t think it’s necessarily more common to have a boar with multiple sows as not everyone has space for a herd.
How old is your sow?
Any bond comes down to character compatibility so it is about finding the right friend for her. If you can contact rescue centres then they should be able to help you with dating her to try to find a new friend.
It is the safest way to ensure she will accept new company.
There can sometimes be a bit of an issue with older sows accepting new company (boar or sow), but it depends very much on the sow - some will accept a new friend, others won’t.
Once sows are past natural pup bearing age they can become unwilling to live with a boar. Also if they have been with a lifelong friend and then lost that friend they can sometimes prefer to not share territory with another. The alternative (but it’s not always possible for everyone) is to have another pair of piggies live in a separate cage but beside the older sow so they have stimulation and interaction between the bars without the pressure of forming a hierarchy and sharing territory
There is a section in this guide entitled ‘cantankerous old age’ which explains a bit further
A Closer Look At Pairs (Boars - Sows - Mixed)