I've seen a number of people use $500k for 20 years, which is also what we did for each of us. It think that is a sweet spot in terms of cost and value. Inflation adjusted $500k then (2015) might be $600k now.
At first we were newly married with few assets, so $500k would have made one person leanFI in our duplex whose rent nearly paid the mortgage. Now we have a lot more assets but a kid, and $500k would still bring the other up to a middling-FI value. The stash will continue to grow, and we will likely have one or two more kids, so it will continue to be about the right amount for a few more years. After about 15 total years it will be superfluous, but will only have a few years left on the policy so I will probably ride it out. Neither the payout nor the premium are inflation adjusted, so it won't be very significant by the end of the term anyhow.
We have all our insurance through state farm. They offer a strong volume discount for having so many different policies through them (home, auto, life, disability), so that I have not been able to find better rates the few times I tried.
Long term disability might be at least as useful. Economically it is at least as devastating, and is also more likely for young people. Use a 6-month or so exclusion period, then maximum allowable amount (60% salary or something) after that.