Lots of good advice upthread. Here are some thoughts from a 63-year-old's perspective.
I was single until I was 54 and earned roughly what you do. I always believed my retirement would be fully self-funded and saved accordingly. I lived in a higher COLA, but my single person townhome was $390k in 2001, so similar to yours, though I've always been a fan of having a mortgage, so I never prepaid it. I was also like you and accumulated cash beyond my automatic savings, because I enjoyed the game of spending less than my paycheck, no matter how much I was sending directly to savings first.
I've been FIRE since 2012 when I got married, but DH has continued to work and we've earned money on our side gig, so I've yet to tap any investments, but as DH edges toward retirement later this year, I've been thinking hard about some of the choices made along the way.
First, I would label that lovely $300k house a "B-o-n-d", then put everything else into equities. At the very least, put all new monies 100% into stocks.
I never did this, because conventional wisdom doesn't offer this advice, which makes conventional wisdom way too conservative IMO. This is especially important for a woman not making an insanely high income who is quite likely to live a very long time in retirement and doesn't want to worry about how she's going to feed herself.
As part of this strategy, I would keep an slightly larger EF. I'd kick it to 20k or even 25k. I would do so to offset the potential volatility of a stock heavy portfolio. The small opportunity cost would be more than offset by market gains, using all of the stock market history as a guide. If the market tanks, you could avoid making any withdrawals for a year or even two with careful planning and frugal living. This would be enough to smooth the ride as the markets recover, which they always do.
I'm tickled to be the first on this thread to suggest the lovely Mr. JL Collins NH's "A Simple Path to Wealth". Read the blog for free and order the book from your library.
One more thing: I understand why you'd be reluctant to do this, but mortgage rates are dropping again. In your shoes, I'd be sorely tempted to take out a cheap-ass 30 year fixed mortgage on the house and invest it in the stock market. It would be a big boost to your retirement savings and you could always pay it off when you fully retire.
Oh, and the creator of cFIREsim is a forum member, which tickles me.