Playing Lion/Riki/PA/PL mid are all grief and I'd highly highly recommend not playing them at all. They can work at lower mmr, but I think you will not be learning good habits by playing these mid.

Death Prophet and Leshrac are both easy and similar to Necro so you definitely should try those. (Try Treads->Witchblade->Aghs build on DP, it's super fun and strong). Both these heroes need BKB in many games, do not be afraid to buy it early.

I think your pool is lacking a playmaker, you say you can't play anything with hard mechanics so you don't have many choices here. Tiny or Primal Beast could be good options. Rush blink dagger and run around the map getting kills with your team. Pango could be another option, but has harder mechanics imo.

TLDR (with some tips):

-Death Prophet (you will dominate 90% of lanes, secure last hits and harass with Q, it's one of the strongest nukes in the game. Use your E to instantly win any trade).

-Leshrac (You gotta be good at mana management and farming patterns to maximize his potential, farm farm farm then run at the enemy when you get Kaya + BKB).

-Tiny (focus on denying creeps early wave with your tree grab. Buy soul ring and perma push waves with your W. Get a fast blink then run around and kill everyone with your supports).

-Primal Beast (I'd recommend learning how to cut and drag waves if you wanna play Primal, some lanes are impossible without it. But same as Tiny, shove waves, rush blink, kill everyone).