I have searched MN and not really found anything suggested that helps, so ended up starting a thread anyway.
Ds2 starts secondary in a couple of weeks. School has strict uniform requirements and he needs two bags. One for everyday school stuff/books etc, the other for PE. They both have to be plain, zipped bags, restrained in colour and without a pattern or obvious logo. (Lack of a logo rules out a huge majority of bags that would have been suitable before I've even started.)
Ds has joint hypermobility syndrome, which can be painful at the best of times. He will be walking a mile to school and back every day, so they need to be comfortable to carry as well. So, I'm thinking a backpack will be the best choice for his main school bag. (We've noticed boys from the school seem to have primarily a mix of backpack and messenger type bags.)
I've seen large rucksacks, like some of the North Face ones, recommended on here, but they are more than we wanted to spend at about £80.00 ish.
Realistically, how much stuff will he be carrying around all day every day? I'm assuming, his backpack will need to be big enough to fit A4 size text books? I seem to remember carrying all my exercise and text books around with me all day (verrry long time ago) but we didn't have lockers.
For his sports bag, if carrying it at the same time as his backpack, he'll need something with handles and a long shoulder strap, so I've been considering something like this which is plain and logo-free, but I'm not sure if it's too big.
He will have a locker, although I was told by the staff member responsible for pupils with healthcare needs that they are particularly small, so may not fit his PE bag.
They have said that if this is a problem he can leave his PE kit in the SEN room though.
I have spent a stupid amount of time looking at bags online and still can't decide - decided to consult MN, only to find the site was down. Spent another day searching and have now come back to see if anyone can help.
Willing to pay more for his backpack, as obviously going to be using it every day and it needs to be comfortable and not a strain on his joints etc, but £80 + is a bit too steep at the moment, given dd's school chose this September to introduce their brand new uniform, just as we have to pay for ds2's secondary kit and ds1, who hasn't grown in ages, suddenly had a spurt and grew out of his compulsory blazer and school-branded PE kit that had lasted him two years. 
Any suggestions would be greatly appreciated.