I can't think of anything that would depress me more than a fwb. It would just high light how I didn't find a real connection that was mutually valuable and exclusive.
If it works for you great but it isn't any sort of answer to finding meaning in the second half of life as a single woman.
I agree with others who've said that financial concerns ARE a restriction. Suggestions to go travelling are a little blinkered if you're in a low to minimum wage job with nobody to shore you up financially.
I am OK now (secure, not wealthy) but I have a decade on the OP. I would think through options that give security. Moving to a cheaper location, buying a two bed place near a station and renting second room out, even for five years, just to get financial security.
Travelling is lovely but realistically one doesn't want to be poverty stricken in old age.
Also, to those saying they understand because they were single once, it is totally different as you age. A lot of married women don't understand that part of the value society places on them is their value as one half of a couple. Having a partner or husband is perceived to be a validation of sorts in our society. Try being single in your late forties and separating your value as a person from your value as a woman. There is a distinction and there is a need to be conscious of your value as a person even if society doesn't view you as a valuable woman. The need to value yourself is paramount. The need to be honest with yourself about the structure of life that you want (career, City/suburb/part time/full time/cats/academia/going hell for leather dating) needs to be thought through very consciously I think.