I would also try nude beaches.
Letting her watch threesome, gangbang and dp porn while eat her pussy and ass and talking about this worked very well for us. One night when I confessed about cuckolding when she was very hot she just openly started to talk about her women dreams desiring multiple men fucking her pussy and ass at once. Then we started with her having yoni massages in salon and recently she had 15y yonger guy fucking her ass in hotel for the first time in our 20 years marriage! After a few years of talking, me showing my support, showing how I like it, wife became very open without hesitation of her women's nature which is cuckolding!
