You can use a backdoor Roth IRA or even a taxable account, but neither of those reduces your tax bill this year. One option you should consider is using a cash balance plan.
A cash balance plan is a type of defined benefit plan (pension) that acts like a defined contribution plan (401K).
Every year, your company (i.e. you if you’re the owner or a partner) makes a contribution toward the cash balance plan, usually at the end of the year on your behalf. That money is invested by your company’s chosen investment manager.
The Pension Protection Act of 2008 now allows the plan to pay the participants the actual returns of the plan instead of the IRS Treasury Rate, with the caveat that the return can’t be less than zero.
Maximum contributions may range from $50K for a 35 year old to $200K for a 65 year old. But many plans, due to actuarial restrictions and top-heavy testing, limit you to much less.