Schwab bought TD Ameritrade last year, which has probably influenced TD Ameritrade's pricing:
https://www.tdameritrade.com/pricing.pageThey now charge $0/ETF or stock, buying or selling. So there's lots of choices for total U.S. stock market ETFs.
If you prefer Vanguard, there's "VTI". I also like iShares, ITOT. Both of those charge 0.03% and hold ~3500 stocks.
Have you considered getting international exposure to equities? Maybe VXUS or IXUS?
You could keep 80% US, but have 20% be international. In prior decades, US and international took turns beating each other, so consider international for diversification.