Thinking about several alternatives, I think for you I'd recommend 100% in ITOT , VTI or SCHB. All are U.S. total stock market ETFs with expense ratios of 0.03%.
You give up international diversification, but in taxable maybe the tax forms for international dividends are more annoying than worthwhile. Also, for international you'd need a second ETF, and you asked about buying an ETF.
An interesting alternative could be a Vanguard Target 2035 mutual fund. It's a mutual fund, not an ETF, as I couldn't find target date ETFs (well, just some charging over 0.70%). Also, it has a bond component that generates income, and means paying tax on that income each year. It would be good to avoid putting bonds in taxable... but with a target date fund, you get everything all in one place. The diversification would be even better: 2/5ths of the equity portion is international.
The thing I don't like, is that 5 years from now, you will still be 100% equities. You'll only have a couple years until you might withdraw money. With a target date fund, you ease into it more gradually. At the target date, the fund reaches 50% bonds / 50% stocks. But it starts at 75% stocks... so you reduce risk as you approach the target date (in this case, 15 years from now). I also only mention Vanguard because when you look for "fidelity 2035" or "schwab 2035" their expense ratios are far higher. I think Fidelity also has a lower cost option, that isn't their first result, so you could track that down.
So go with 100% ITOT / SCHB / VTI , but ideally you'd reduce your equity allocation over time, even though you have a wide range of years for possibly withdrawing money.