You need to correct your failure to file the required 2018 Form 8606. Line 14 of the 2018 Form 8606 will carry forward to line 2 of your 2019 Form 8606 to be used in calculating the taxable amount of any traditional IRA distributions, including Roth conversions, made in 2019.
The only way under the law to "unmix" your basis in nondeductible traditional IRA contributions from the pre-tax money in your traditional IRAs is to roll over all of the pre-tax money in all your traditional IRAs to a qualified retirement plan like a 401(k), then convert the basis to Roth. Rollovers from a traditional IRA to a qualified retirement plan can only be from the pre-tax money in your traditional IRAs, so this rollover leaves only the basis in your traditional IRAs. The result must be that at year-end you have $0 in traditional IRAs.
The other option is to just convert every thing to Roth over the next few years. With 30 years until retirement, the long-term benefit of tax-free growth in the Roth IRA instead of taxable growth in the traditional IRA is likely to far outweigh the deferring of the taxable income. You also have a relatively short time until the tax rates now in effect revert to what they were before 2018.
