I think I made too much ambiguity in my diagram, R5 and R4 don't really exist, and R3 isn't part of the relay coil, it's a real resistor though since RL1 isn't a real relay, R3 doesn't have a proper value either. The sense resistor I chose the value for proof of concept, rather than based on real life, I'd actually be using 0R33 there. Also it's a small motor from a printer, when it drew enough to blow my H-bridge I was really surprised. Anyho, good point about the LPF, I hadn't thought of that - is a large cap across the sense resistor enough in this case? I agree an IC would be simpler to use - I ended up with this because I was trying to use a single transistor and found the gain wasn't high enough.
Interesting point about D1, I didn't think it would cause a slowdown. The idea is so the cap can be charged, but can only discharge through the relay and it's dropper resistor (which gives it a little bit longer to pull in)
But, since you mentioned a PTC, I think that is the obvious answer, really - I should just pop in a 2A polyfuse and be done with it!