So you’ve got next to no experience using almost anything but Harrow. And your pool of weapons is rather limited, as well, being that you’re around MR6-7.
I would honestly recommend farming the other Warframes on planets you have access to. Using only one thing or gear setup is going to make the game really boring really fast. Variety is one of Warframe’s strong suits.
Well the first that come to mind here are Valkyr, Mesa, Chroma (when you have better mods and about 3+ forma to spare), and Nidus.
Valkyr has the highest armor rating in the game, and the ability to boost it even further with her Warcry ability, which also boosts melee attack speed. Makes her a really tanky blender. Her 4th skill, Hysteria, is pretty much one of the most powerful melee weapons in Warframe. She is also invincible while using it and it provides lifesteal, so it can be used to take down really tough targets or clear a room or two to keep you alive.
You know Mesa’s abilities. her 2,3, and 4 and really good. Shatershield giving 95% DR is insane, and Peacemaker is super strong.
Chroma can give himself incredible damage boosts and reduction. Though he needs a TON of work to make him able to do that, so I do not recommend him yet. Not until you and Tsathy are further along the game.
You also know Nidus, from what I recall. He’s tanky, he has awesome damage, and all of his abilities are useful.
But with the large variations in Warframes, there’s so few that fit all 3 requirements. Nezha, as an example, has something called Warding Halo, which is an excellent defensive ability. His other 3 skills are also all good, and he has the capacity to heal himself and the team. However, only one of them does any damage worth a damn and it’s rather expensive to cast as his ultimate ability.
Many things have 1 or 2 of those traits, but what you describe is basically just a well-made, well-balanced DPS+tank with abilities you like using. Warframe, not being class-based or having elective skills, has almost nothing that fits your criteria exactly.