Here's the problem:
The bridge is so far back on my E string that the string bends up to the saddle quite steeply. At the point where the string is in contact with the back of the saddle, it does not bend back down to rest on the whole of the groove in the saddle. Instead, it resonates from the back of the saddle and hits against the front of it as I play low notes on the E string.

I have a pretty good idea of what needs to happen to eliminate this buzz, the string needs to bend more sharly so that it rests on the whole saddle and resonates from the front but I don't know what the best option is.

I do not want to move the saddle forward because the 12th fret note is still sharp: In fact, I would like to move the saddle back even further to get the intonation right.

The bass cost £150 so doing some modifications myself will not cause any problems.

Should I drill another hole higher up on the bridge so that the string isn't pushed beyond it's limits of flexibility and rests on the saddle at an more comfortable angle?

Should I file down the saddle so that the string can rest on it diagonally and bend over a longer distance.

Alternatively, should I find some way to tilt the saddle backwards?

Will the strings get floppier and solve the problem on their own?

Should I buy some round core strings, because I've heard that they are floppier? The problem with this solution is that I like my strings and action. I also can't afford a better bass.

All help will be greatly appreciated

Here is a diagram to help explain the problem
you could maybe try slightly thinner strings? i had a similar problem when i fitted a .140 gauge on my bass for drop A tuning, when i went down to a .135 it seemed to be sorted.
i know you said you are happy with your strings, but i'm not sure what else to suggest to be honest :\

oh and kudos on the diagram :p
I forgot to mention that I am currently 'working' on a plan.
I hope that the string will wear down the bridge a bit and sort the problem on it's own.

Thanks to moody git for your suggestion. I am currently using a .135, I could go lower but I like high tension for double slapping in particular but also for anything fast with fingers.

I think using tapered strings may help but I don't like spending money and I've just bought a new set, in addition to the ones on my bass