How best to insulate a steel beam...

[iSelfBuild]

Never done a steel opening before (my house is still standing thankfully) but I'm not really sure how best to insulate... or fire board it.

 

The column on the right is embedded in the old cavity (un insulated 55mm common brick cavity... looking at the workmanship and snots/ties it would be a bad idea to get blown in insulation) and the new 100mm block cavity has 90mm T+G Kingspan. On the right I was thinking 10mm aerogel, then fireboard over it. Insulated plasterboard is going left and right to give a flush finish and hide the column. The top of the beam.. stupidly I haven't factored in any room for aerogel or insulating... it's flush with the 1st floor/ceiling joists and depending if I have enough ceiling height... I will see if I can fit 10mm aerogel in but I will then have to pack down the rest of the ceiling to match in the old part of the house (new part is a cold roof and being insulated underneath anyway. I believe I need to fully encase the beam in 15mm fireboard... up the internal side, along the bottom face , then the other side has a timber trimmer bolted on and floor joist hangers, should I just go up and notch between every floor joist and hanger? The column on the left is internal so less issues with cold bridging (granted I know it's one big cold bridge and where it's bolted on pads...