I think there's little room for negotiation here. These things happen during air travel and frankly the compensation offers you got are outstanding. The voucher seems to be the best option. Depending on the route and the season, PE cabins can be a fortune especially if booking last minute. The 75,000 points is also incredible, a meager valuation would be £750. Although perhaps not great if you're not a frequent flier or particularly points savvy. The reason I say there's not much room for negotiation is because they are only required to pay you £260. The offers they've given you are out of the goodness of their hearts. I think the chance of you getting a voucher/points and £260 is slim to none.

However, the worst they could say is no so always worth a try