At first glance, it seems strange that your accountant would recommend you file separately. Typically, couples with one spouse as a high earner and the other as a low earner benefit from filing jointly. Maybe there are factors at play I’m not aware of, but I would double-check that this is the right move.
For w-2 employees, unfortunately options to reduce taxable income are limited. A lot of the options available to the self-employed (business deductions, $56k 401k limit, etc.) aren’t available to you. Sounds like you’re mostly doing the right things. Buying a more expensive house just to write off more mortgage interest usually isn’t a smart move.
You should, however, make sure you and your spouse are doing Backdoor Roth IRAs. It doesn’t save you income tax now but it’s another $12k/year that will never be taxed again. Make sure your taxable investments are tax-efficient- muni bonds, passive stock funds, maybe look at tax-managed funds. A taxable yield of ~2% or less is a good goal. I would also max out the HSA at $7k/year. If you don’t spend it on medical expenses, it works like an ira, and can be withdrawn penalty free after age 65.
I would think carefully about the deferred compensation plan- it does exactly what you want. The fact that the money is exposed to your employers creditors is a negative, but that’s true of all pensions. Is there a reason to think your employer is unusually vulnerable? You could do a probabilistic calculation- figure out how much the pension plan will save you, and how much you stand to lose if the employer defaults, and put a probability on the default. For example, if you stand to save $100k if the pension remains liquid, and lose $1M if they default, there would have to be a >10% chance of default for it to be a bad move to contribute. 10% chance of an employer defaulting on their pension is really high, although see what the numbers work out for you.
Edit: It's important for you (and readers) to understand the difference between the Backdoor Roth IRA and the Mega Backdoor Roth. The Backdoor Roth IRA is through an IRA, so you control it. There's basically no reason not to do it (assuming you can afford to save the $12k per year, and it sounds like you can). The only obstacle that hangs up some people is having a large Traditional IRA balance. But if you do, just roll it into your 401k at work, and problem solved.
The Mega Backdoor Roth has some similarities, but it's with a 401k instead of an IRA. It's rare because it requires your 401k provider to offer the option to make after-tax contributions, and also in-service Roth conversions. You can investigate with your 401k provider, but only a small percentage of 401k providers allow it, so I wouldn't get your hopes up. But if it does work for you, you can potentially contribute up to $56k minus the ~$29k you and your employer put in, so about $27k.