Compact abs exerciser with high(ish) resistance?

geebusuk

I still have to limit what I do with my shoulders, which means no holding weights behind my head for weighted situps - also, basically no other weights of any kind at all .

However, I've worked out I can do weighted situps with the weights on my chest.
However, I've just tried upping the weight and found I can fairly easily do 3 x 12 reps with 35kg on my chest (20kg + 15kg). So to decently push it, it's going to get to being a bit of a faff, piling weights up.

Are there any, perhaps sprung or resistance band based machines that can do a decent weights situp/crunch/similar that don't require arms held high (or much other use of arms - holding weights on my chest has been fine, as I can isolate shoulders okay.)