A "healthy" tan is more of a social desirability thing more than a health thing. Most fair skinned people only need about 10 minutes of sunlight each day, and darker skinned people only need about 15 minutes.
Once you get that, you don't really need any more sun. And it rarely hurts to apply sunscreen, but it can certainly help.
I'll add this link though, if you really want to use a tanning bed. The National Institutes of Health tends to be pretty legit:
"The factors that affect UV radiation exposure and research to date on the amount of sun exposure needed to maintain adequate vitamin D levels make it difficult to provide general guidelines. It has been suggested by some vitamin D researchers, for example, that approximately 5–30 minutes of sun exposure between 10 AM and 3 PM at least twice a week to the face, arms, legs, or back without sunscreen usually lead to sufficient vitamin D synthesis and that the moderate use of commercial tanning beds that emit 2%–6% UVB radiation is also effective [6,20]. Individuals with limited sun exposure need to include good sources of vitamin D in their diet or take a supplement to achieve recommended levels of intake."
Note that it does say "moderate use," so you may want to do more research and gauge what tanning bed exposure times equate to those 5-30 minutes.
I also noticed you said "Indoor tanning" over "tanning beds." To be honest, there's probably no difference if you're talking health. The CDC says neither is healthy, and there is no other entity that's more highly regarded perhaps short of the World Health Organization.
But if you're set on tanning even with the warning, (I wouldn't suggest paying for it):
One obvious "plus" for tanning beds is that you can easily get a tan over normally exposed parts of your without being indecent or having people stare at you. Just being outside, you can probably just get it for your lower and arms and legs. That's a problem if you live in an apartment or something and don't feel comfortable laying out in a bikini.
Of course, the sun is free. You might be able to open up a window in your place and lay out naked.
In either case, I would keep health in mind. Tans are generally a bad sign for skin with regards to health. So whether it's the sun or a tanning bed, don't get "addicted" to getting really tanned.