LC:
Check seforim stores. There are several siddurim that have rather large fonts, and there are also several prints of siddur that are made with really large letters to accommodate those Yidden whose eyesight ain’t great anymore. (There are siddurim from many publishers that are made for the baalei tefiloh and are generally oversized versions of their regular publications.) Those made for the blind (legally blind) are quite limited, but are nevertheless available. Since most publishers do not make these, there is far less choice regarding nusach.