Pretty much any arrangement can be bound contractually. In your case it may be worthwhile to consider becoming tennants in common on title. This protects the interests of your mother and your own interests if you are either tipping in cash or asking the bank to do so on your behalf. Later, if the property is sold in whole or part the owners on title are each entitled to a share of the gain according to their portion of ownership. There are of course more complicated trust structures that would allow the benefits to be funneled as the trustee (or trustee company) sees fit.

These are not simple structures, so make sure you get sound advice.
And good luck.