Shall I put ISA cash savings into Stock ISA’s?

I’m a 31 year old woman, saving for my second house (which I will be buying with my husband).

I currently have maxed out my ISA limit for this tax year. 19.5k as cash and 1k investment.

Should I transfer my 19.5k into the investments too?

For background I have only invested in S&P 500.

I have an additional 10k saved up which I will transfer to investments in April.

Many thanks.