Old Flat Roof replace ore repair

Hi,

I started to develop a small leak in the old flat roof which covers 1 bedroom, the kitchen and the bathroom. The old roof is made up of zinc, and the various roofers are recommending I replace versus patch up the roof. Apparently the roof was patched a few times before I purchased the property in 2013.

The choice I am getting is either GRP versus felt, felt is about 1000 cheaper than felt but the roofer says it lasts longer time and is less likely to have issues.

So far options are:
300 gbp to patch
1500 gbp to replace with felt
2500 gbp to replace with grp

This is not costing the option of putting extra insulation, as one bedroom is really cold as there is no insulation against the current roof.

Time is not ideal as I was going to redo the bathroom this year, but wanted to get people's input/feedback with roofing repair choices.