Pleated blind DIY stay mechanism - advice required

[Osem]

I recently bought some pleated cellular blinds for our Velux windows from Ikea. The metal top rail is fixed to the window frame via brackets but the blind is designed to hang vertically as opposed to the pitch of a roof. I have trimmed the fabric and rails so that the blinds sit neatly inside the frames of the hinged window openers but need a secure way to fix the bottom rail at various heights thereby varying the amount of light allowed through the window. Luckily the wooden window frames taper inwards slightly which means that if I simply push the bottom rail back towards the glass it will hold itself in position. However this does create indentations in the wood so I'd prefer to come up with an alternative means to keep the blinds closed and in the right position.

There are no external cords and the blinds rise/fall simply by raising/lowering the bottom rail but are weighted so they do stay in position at any height when allowed to hang. All I need, therefore, is a simple means by which I can locate the bottom rail in various positions up/down the sides of the window frame. Some sort of sprung or friction based mechanism at either end of the bottom rail would work but it would need to be simple and unobtrusive.

Any thoughts gratefully received.

TIA

Our Velux windows have wooden rails down either side with four stopping points, allowing the blind to rest against the glass and be either partially or fully closed.

The rails are not integral to the frame and are held in place with small brass nails. They were installed by the previous owners and I have always assumed they came as part of a kit with the blinds. However I'm sure you could find something similar on the interwebs or maybe even fashion your own if you're handy at woodwork.

If you find any to buy, let me know, as you can see ours are starting to get a bit mildewy and I'd like to replace them.

[Osem]

Thanks. That's a possibility I'd considered since my OP and I do have some nicely matching wooden strips from an old louvre door which wouldn't need much doing to them to fit unobtrusively. Gravity would hold the blind in position at the correct height, the only role the wood strips would play would be keeping it nicely parallel to the window so they'd need to be the other side of the blind from the arrangement on your window.

Our windows are 20 years old now and have stood up very well to the elements. They are suffering from the mildew problem on the inside of the frame though and I promised myself I'd clean, sand and retreat them this year. Mind you, I said that last year too...