Why do you think you have limited space?
I included ours as simple printed (typed) letters, in English, signed, with contact info.
But: since these are not formal requirements or documents, there is no obvious reason why they would not accept, for example, a printed email. Particularly if you included, for example, a short letter of explanation explaining that getting signed versions was not practical or whatever other explanation.
However, would recommend you be extra careful to include contact information (email, address, telephone number). The letters only help your case if they are credible and verifiable if need be. I'd also suggest that for those you include, it may help if the senders have online profiles that can also be checked - for example, facebook or linkedin or whatever. And e.g. email addresses that are linked to e.g. professional accounts, and not just [seriesofnumbers] @ yakhoo.
I'm sure you see what I mean - if an officer looks at an email letter and can sort-of verify who the person is online in a few minutes, that's one thing, if it's from some dodgy email account and a person who is not on any social media, it may not add much. They still seem to prefer signed docs and if you're going to depart from that, make sure it adds to your case. Quality over quantity.
(I say this as someone who rarely uses most social media and neither does my spouse - but I have used social media/internet to confirm who people are for work purposes from time to time)