Actually, if OP does not need the money, the best time to invest is when the market is shaky. Any short term volatility is just paper losses and does not affect the OP as she waits for the upswing.
I'm not convinced. It's difficult even for the experts to time the bottom of the market. I was writing a report on stock market crashes a few weeks ago and there were something like 30 short lived rallies in the Nasdaq during the global financial crisis crash. It took 4 years for the Nasdaq for recover its losses.
I'm a big fan of investing in equities. As others have said, you're losing money in real terms in a savings account given inflation is so high. I have an interest only mortgage backed by my ISA investments and I typically make 25-30% a year.
But two things make me nervous when friends ask for investment advice, Bonds had their worst year in pretty much living history last year, falling by 30% globally (as did the Nasdaq in the U.S.) and 40% in the U.K. It was the first time bonds and equities fell together in 30 odd years. That makes a traditional balanced portfolio difficult without the safe haven element.
Secondly, I speak to fund managers regularly for work and they're nervous. The message from a few is that double digit returns from equities are unlikely for the next few years at least. They seem more confident in U.K. valuations than the US but it's not easy money at the moment. Inflation needs to come down in the U.K. and we need to bounce out of recession, if we hit it (as forecast). Yes, the likes of Tesla and Nvidia have performed well this year but that's on the back of big losses last year.
But monthly investing is definitely one option. It allows you to drip feed your money in and get the average in price over a longer period. And I'd go for an actively managed U.K. and global fund with £10k, with a few more interesting side investments.