Marmolada glacier is easy and not so wide, but... It's a glacier and there are many crevasses, even though you can't see (they are covered in snow: the most dangerous one!)

I think if you don't have experience of roped glacier travel, it's better if you take a guide.

Usually the glacier is crossed by a well marked track, and dozens of people pass there every day with good weather...

If you go without a guide, quite surely you'll survive but you get a little risk, and my advise it's to go with someone experienced of glaciers (I remember that, 10/15 years ago, a strong italian climber, climbed up from an extreme-route of south face, fall in a crevasse and died descending from normal route... He was a very experienced mountaineers, but he went without rope...)

Ciao

You will not get a guide merely to get you across the glacier (after all you have to return that way). It's all or nothing. Either get some training so you can do this on your own, or invest in a guide to help you do this climb safely. You will also receive valuable training to use on your next climbs.