I hope your real life issues resolve
I'm trapped at home with four kids, two of them special needs (ADHD, ODD, etc.). Until I go back to work, that ain't happening.
So, thus far we have mention of larger Streak launchers, a mid-size AC, two new engine concepts (one I would suggest for small craft, like my FighterShip concept), better pulse lasers, more blazers and flamers, DFM-launchers, a new armor concept.
I have homebrew tech here on the forum you could look up you could use - why not post something over at the OF asking for suggestions? God knows everybody is probably also bored as heck.
Just as a preliminary;
1.5 t/2 missiles; following the progression gets you an 8-P for 6 tons and 10-P for 7.5. I'd be leery of anything bigger, but you might go one more for 9 tons.
AC/15 and some other stuff;
https://bg.battletech.com/forums/index.php?topic=12121.0Horizontally Mounted Engines - A fundamental reordering of the BattleMech's interior on par with the Torso Mounted Cockpit was considered possible but unwarranted by designers whose maintenance and cost issues would be much more than normal.
Dual Fusion Engines - Building on the Horizontal Mounts this innovation allows BattleMechs to utilize two Engines each spaced out over the torsos working as one. Two 200 Fusion Engines would equal a 400 and of course would need a four ton gyro in order to balance things out. [Granted this is far off and needs work]
Enhanced Pulse Lasers - somehow improve the ranges on InnerSphere models
Large, Medium, and Small Flamers -