401k is the way to go if your employer offers it. If you're self-employed (and w/o payroll employees) you could open a solo-401k for yourself as well as your spouse. Otherwise, you could also do an IRA. Actually, in any case you could also do an IRA if you have extra income to spare. With an IRA, mutual funds are probably the easiest/safest way to invest.
If it's an employer 401k, you usually have no choice on who manages it. With the others, you could choose an actual person or a robo-advisor (basically, a computer program which monitors your account and does the various trades). Robo-advisors are generally cheaper, and they work fairly well. However, not all investment firms offer it.
Generally, easiest way to to split up investments is via "target-date", most firms offer that in one form or another. Basically, you go through an online interview, state when you plan to retire, how comfortable you are with various swings in the market, so forth, and your account manager (robot or human), splits your investment between stocks, bonds, and cash accordingly. Stocks are risky, bonds not so much. The inverse to that is that stocks bring bigger potential returns whereas bonds give you smaller returns. Target-date investing splits all that up so that you're more in stocks when you're farther away from retirement, and mostly bonds when you're closer to start drawing your retirement income. But if you want to play it safe, you could ride it mostly bonds the whole way through...the interview process I mentioned above factors that in. And also you're not stuck with it, you could change the split whenever you want by retaking the interview.
I'm no expert, I may be wrong on some of that, but I'm pretty sure I'm close. Personally, I have a solo-401k which is robo-advised. I have an E-trade account for that. It's not the cheapest in terms of account fees, but they were one of the few who offered solo-401k's at the time, so I just stayed with them.
Don't be afraid of it, it's really not all that complicated nowadays with these programs, and you don't need to know all the minute details and be able to read the daily stock reports like serious investors do. I still don't. Basically, end of the day, if you see dow/nasdaq/s&p in the red, that's bad. In the green, you're good.